Ghusl (Major Ablution)
Ghusl means major canonical ablution or a complete washing of the body. It becomes obligatory after sexual intercourse, even if only the head of the penis disappears into the vagina. Any discharge of semen, and the completion of menses and post-childbirth bleeding.
Taking ghusl every Friday before the congregational prayer is highly advisable, for the Prophet always did so. Before beginning ghusl, one should make the intention to perform it and, if one will pray after performing it, also the prayer.
Things Forbidden to a Ritually Impure Person
People who are in this state cannot pray, circumambulate the Ka'ba (tawaf), enter a mosque or place of worship unless necessary, or touch the Qur'an or any of its verses except with a clean cloth or something similar.
What Makes One's Ghusl Valid?
Rinsing the mouth thoroughly so that all of its parts are cleaned properly.
Rinsing the nose right up to the nasal bone.
Washing all bodily parts thoroughly, including the hair.
The best way to perform ghusl is as follows:
Having the intention (niyyat) to cleanse the body from (ritual) impurity while washing oneself.
Washing the hands up to the wrists three times.
Washing the private parts thoroughly.
Removing all filth from all bodily parts.
Performing ablution.
Washing all bodily parts three times, including the hair thoroughly. No part, even the size of a pinpoint, is allowed to remain dry. Rubbing and pressing the body is not obligatory.
source
http://www.thewaytotruth.org/pillars/tahara.html