When is ghusl required?
Short answer: After intercourse or ejaculation, at the end of menstruation and post-natal bleeding, and (according to many scholars) on accepting Islam.
Ghusl (the full ritual bath) becomes obligatory after sexual intercourse or a discharge of semen (including a wet dream), at the end of menstruation and post-natal bleeding, and on accepting Islam according to many scholars. The deceased Muslim is also washed. It is Sunnah for Jumu‘ah and the two Eids. Learn how to perform ghusl.
Answered according to the Quran and authentic Sunnah as explained by the scholars of Ahl al-Sunnah wal-Jama‘ah. For your own situation, ask a trusted scholar.