From my basic understanding, 'It has done' is an incomplete sentence. What comes after done in this sentence is what 'It' has completed. Has done is the present perfect tense of to do. 'It is done' is saying that 'It', the subject of the sentence, is done.

Yes, all of these are correct.

In what context do you mean? There can be several different ways to say that depending on the context behind it.

It all depends on what type of movie you are interested in watching. Kids movies tend to be easier to understand for english beginers.