The word "done" is the past participle of "do," but you can use it as an adjective to describe that something or someone is finished (What is an adjective?).
Generally, "done" means that something is finished:
The turkey is done. Take it out of the oven.
She's done. You can talk to her now.
Are you done? Can I take your plate?
The work is finally done.
Done! (I'm finished.)
You can use an "ing word"* after "done."
They're done swimming for the day.
She's done talking.
I'm done eating.
They'll be done baking in about half an hour.
Some people might not like the way these sentences sound, but this is the way Americans speak.
The word "done" takes on a more subtle meaning that would be easier to understand if you know something about the situation in which "done" is used:
They're done. (Their relationship is over.)
She's done with him. (She doesn't like him any more.)
My work here is done. (I have fixed the problem.)
Are you done? (Someone talks and talks and talk and makes another person angry. When that person finally stops talking, this is the question that might be asked.)
That's something that's not done here. (That behavior is not appropriate. This could also be considered passive voice.)
Occassionally, you'll hear "done" used incorrectly. The speaker may or may not realize the mistake. These are examples of poor English:
She done quit her job.
He done good. (He did something good.)
Here's a video for more explanation:
I'm done.
(*Is it a gerund or present participle? I'm not sure, but we can safely say "ing word.")