Ghusl is required after sexual intercourse or any sexual discharge including a wet dream, after menstrual periods and after postnatal bleeding. Like in the case of Wudoo, it is preferable to perform the Ghusl in the way that the Prophet (PBUH) performed it.
However, the bare minimum requirement for a valid Ghusl are to make the intention for Ghusl and then thoroughly wet the entire body. So if you made the intention and then jumped into a swimming pool and got completely wet, the Ghusl is valid. However, it is much more preferable to follow the way of the Prophet PBUH) as described below.
Steps in Performing the Ghusl
1. Make the intention
2. If Ghusl is being done after intercourse, wash both hands, then wash genitals with the left hand.
3. Do full Wudoo
4. Rinse your mouth and your nose (by sniffing up water, IF you have not already done it as part of Wudoo)
5. Wash your entire body. Make sure water reaches every part. Rub the water with your fingers into the skin under the beard and hair. Also pour some water over your head (If you have tightly braided hair, you do not need to open the braids—just pour three handfuls of water over your head).