1) IT HAS NOT BEEN DONE YET = Something has never been done (it might still be done, sometime in the future). EX: A person has not yet walked on Mars. It has not been done, yet..............................
2) (makes no sense) but you might rephrase it with different meanings ...................(2a: It has not done anything yet = It has had no effect, yet) .... (2b: It is not done yet = It (ex: a cake) is not yet finished... maybe it is baking and it will be fully baked 10 minutes from now, but it is not done yet)