Ghusl is washing the entire body with water.

Allah say:
"O you who believe! Approach not As-Salat (the prayer) when you are in a drunken state until you know (the meaning) of what you utter, nor when you are in a state of Janaba, (i.e. in a state of sexual impurity and have not yet taken a bath) except when travelling on the road (without enough water, or just passing through a mosque), till you wash your whole body. And if you are ill, or on a journey, or one of you comes after answering the call of nature, or you have been in contact with women (by sexual relations) and you find no water, perform Tayammum with clean earth and rub therewith your faces and hands (Tayammum) . Truly, Allah is Ever Oft-Pardoning, Oft-Forgiving." (Quran 4:43)



Occasions when Ghusl is Required as an obligatory Act
Ghusl is obligatory on a person in the following cases:

If there is discharge of semen due to stimulation or because of an erotic dream (wet dream). If a woman finds her self wet due to an erotic dream then Ghusl is obligatory on her because of the hadeeth of Umm Salamah, who reported that Umm Sulaim, the wife of Abu Talha, asked Allah's Messenger (sallAllaahu 'alayhi wa sallam), saying: "Allaah is not shy when it comes to the truth. So is it obligatory for a woman to perform ghusl if she has a wet dream (i.e. seminal fluid comes out)? The Prophet (sallAllaahu 'alayhi wa sallam) responded: "Yes, if she sees the fluid." This hadeeth is reported by Al-Bukhaaree and Muslim. However, if one has an erotic dream but no wetness is found then ghusl is not obligatory
Ghusl is obligatory for men and women after sexual intercourse performing Ghusl is required regardless of whether the person ejaculated or not. A male is required to perform ghusl if the head of his penis entered the Vagina of the female even if it was for just a secound. Abu Hurairah (radyAllaahu anhu) said: Allah's Messenger (sallAllaahu 'alayhi wa sallam) said: "When a man sits in between the four parts of a woman and enters into her (for intercourse), the ghusl becomes obligatory." Reported by Al-Bukhaaree and Muslim. In Muslim's report, there is the addition: "even if he doesn't ejaculate. The same ruling applies to the woman.
Females are required to perform ghusl when their menstruation period end.
Females are required to perform ghusl at the end of their post-childbirth bleeding. If she continues to sleep for more than 39 days then she must perform ghusl at the end of the 40th day.
It is required to perform ghusl on a Muslim who has died but if the Muslim died in Jihad (i.e as a Shaheed or Martyr) then no qhusl is required.
Occasions for which Ghusl is preferred
Ghusl is recommended in the following cases:

Before going to Jummah Congregational (Friday Prayer).
Before going to Eid Prayers (Muslim annual feast prayers).
Before undertaking Umrah or Hajj (Pilgrimage to Makkah).
Upon washing a corpse. (According to many scholars, the performance of Ghusl is preferred for a person who washes a corpse).
When a disbeliever converts to Islam.
How to Perform Ghusl
The Complete Ghusl: which is what has been reported in the hadeeth of "Aishah (radyAllaahu anhaa) in Al-Bukhaaree and Muslim, in which she said: "When Allah'ss Messenger (sallAllaahu 'alayhi wa sallam) would perform ghusl due to Janaabah (sexual impurity), he would begin by washing his hands. Then he would pour water from his right hand to his left and wash his private parts with it (i.e. the left hand). Then he would perform wudoo (ablution). Then he would take water and place his (wet) fingers on the roots off his hair. Then he would pour three handfuls of water over his head. Then he would pour water all over the rest of his body. Then he would wash his feet." This wording is from Muslim. The hadeeth is in Al-Bukhaaree and Muslim from the narration of Maymoonah, (radyAllaahu anhaa).

Special Note for women

The Ghusl for men and women is essential same. Women who have braids can do ghusl without having to undo their hair if they are in Jannabah (sexual impurity). However if they are impure due to Menstruation or Nifass (post Natel bleeding ) then they should open their hair before doing ghusl. (see Hadiths Below).

Also if the Muslim female is making ghusl after the end of her Menstruation or Nifass (post Natel bleeding ) then after the ghusl (described Below) she should take a piece a cloth perfumed with musk and clean the private parts with it thrice.

Thus apart from this there is no difference in the way men and women perform Ghusl.

The Ghusl for men and women is as follows:





1 Intention inside ones heart not verbal.
2 Say Bismillah
3 Wash the right hand up to and including the wrists. Make sure to while rub and rub between the fingers of the hand. And thus make sure no part of the hand is left dry. Three times


Then do the same with the left hand. (also three times)

4 Wash off the impurities (off the private parts)


5
Wash the right hand up to and including the wrists. Make sure to while rub and rub between the fingers of the hand. And thus make sure no part of the hand is left dry. Three times



Then do the same with the left hand. (also three times)

6
Make a cup with the right hand then from this hand take water into your mouth and swirl it inside the mouth and then expel out of mouth. then sniff remaining water from the cupped right hand and sniff water into the nose and then blow the water out and using the left hand remove the water from your nose. Do this three times



Some people rinse the mouth first three times and then rinse the nose three times

However the first method is the most authentic.



7 Wash the face three times, from the hairline to the jawbone and chin, and from start of the ear to start of the ear.
After this a man should wash the hair of his beard by taking a handful of water and entering it below his chin and rubbing it through his beard and passing the wet fingers through the beard. (once)

8 Wash the right arm up to and including the elbow Three times.
The arm extends from the fingertips, including the nails, to the lower part of the upper arm. It is essential to remove anything stuck to the hands before washing them, such as dough, mud, paint, nail polish etc, that could prevent the water from reaching the skin

.
Do the same with the LEFT ARM . Three times

9 Pour water over the head Three times down to the roots of the hairs. rubbing the roots of the hair with the wet fingers
10 Pour water liberally over the entire body, beginning with the right side and then the left side. Then pour water over your head. (Ensuring that no part of the body is untouched by water by rubbing the body with your hands)
11 Move away from area were you did ghusl and Wash the right feet up to and including the ankles, three times,
You should enter the water between the toes with your little finger and then wash the feet (note not wipe feet but wash them) and make sure and make sure you wash the sole of the foot and the heals. Make sure no parts of the foot is left dry

Wash the left foot in the same manner as the right foot. Three times



12 Then say the following Duas for Wudhu when outside the bathroom (if bathroom has a toilet inside it)

Ashhadu an laa ilaaha ill-Allaah wahdahu laa shareeka lah, wa ashhadu anna Muhammadan abduhu wa rasooluhu.

( I bear witness that there is no god except Allaah alone, with no partner or associate, and I bear witness that Muhammad is His slave and Messenger.)

Allaahumm aj alni min al-tawwaabeena waj alni min al-mutatahhireena

( O Allah, make me one of those who repent and make me one of those who purify themselves)



Hadiths regarding women's ghusl:


Umm Salamah (may Allaah be pleased with her), who said: "I said, "O Messenger of Allaah, I am a woman who wears her hair in braids. Do I have to undo my braids when I make ghusl because of janaabah? He said, "No, it is enough if you pour water on your head three times, and then over the rest of your body. That will make you clean." (Reported by Muslim, no. 497).
Narrated 'Aisha: In the last Hajj of Allah's Apostle I assume the Ihram for Hajj along with Allah Apostle. I was one of those who intended Tamattu' (to perform Hajj an 'Umra) and did not take the Hadi (animal for sacrifice) with me. I got my menses and was not clean till the night of 'Arafa I said, "O Allah's Apostle! It is the night of the day of 'Arafat and I intended to perform the Hajj Tamattu' with 'Umra Allah's Apostle told me to undo my hair and comb it and to postpone the 'Umra. I did the same and completed the Hajj. On the night of Al-Hasba (i.e. place outside Mecca where the pilgrims go after finishing all the ceremonies Hajj at Mina) he (the Prophet ordered 'Abdur Rahman ('Aisha's brother) to take me to At-Tan'im to assume the lhram for'Umra in lieu of that of Hajj-atTamattu' which I had intended to perform (Bukhari Volume 1, Book 6, Number 313:)

Narrated 'Aisha: An Ansari woman asked the Prophet how to take a bath after finishing from the menses. He replied, "Take a piece a cloth perfumed with musk and clean the private parts with it thrice." The Prophet felt shy and turned his face. So pulled her to me and told her what the Prophet meant. (Bukhari Volume 1, Book 6, Number 312:)