When is ghusl (full ritual ablution) required, and how is ghusl performed according to the Sunnah?

Ghusl is a special purification performed by washing the entire body, including the mouth and nose, to remove states of ritual impurity such as janabah (major ritual impurity), menstruation, and postpartum bleeding. In the Qur’an, it is stated: “If you are in a state of janabah, then purify yourselves (by washing).” (an-Nisā’, 4/43; al-Mā’idah, 5/6). In the Sunnah of the Prophet (peace be upon him), it is also commanded to perform ghusl after experiencing a wet dream, sexual intercourse, or after the completion of menstruation and postpartum bleeding. (Bukhari, Ghusl, 22, 28 [282, 291]; Muslim, Hayd, 87-88 [348-349]; Abu Dawud, Taharah, 118, 127 [314, 359])

Ghusl is performed by rinsing the mouth thoroughly, sniffing water into the nose, and washing the entire body so that no part remains dry. According to the Hanafi school, these are the obligatory acts (fard) of ghusl. If any of these are omitted, the ghusl is invalid. In addition to these obligatory acts, there are also recommended (sunnah) practices of ghusl.

When performed according to the Sunnah, ghusl is done as follows:

The person intending to perform ghusl makes the intention and says “Bismillah” (in the name of Allah). He washes his hands, removes any physical impurity from his body if present, and washes his private parts. Then, using the right hand, he rinses the mouth three times thoroughly, then sniffs water into the nose three times and cleans it, and completes wudu (ablution) as for prayer. After that, he washes the entire body thoroughly. If water collects where he is bathing, he washes his feet at the end to complete the ghusl.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu