Can you please tell me the difference between Marja, Ayatollah, Mujtahideen and Ulama

Marjie: A mujtahid who publishes his Manuel of Islamic laws and declares he can be followed

Ayatollah: Sign of Allah. A person who has reached ijtihad

Mujtahid: a scholar who reaches ijtihad, meaning they can extrapolate islamic law from Quran and Hadith etc (after studying for many years)

Ulema: comes from Arabic alim, ie knowledgeable person