Done is the past participle of the verb "do". It can mean:
1. Completed or finished (e.g. "I'm done with my homework")
2. Cooked thoroughly (e.g. "The steak is done")
3. Socially acceptable (e.g. "That's just not done")
4. Exhausted or worn out (e.g. "I'm done after that workout")
5. In informal contexts, can mean "in trouble" (e.g. "You're done for!")