Questions

I have several questions which I have faced when revising Grammar, I hope you can help me with.
1-What do we mean with the unreal future?
2-In offer should I use will or shall?
3-What's the difference between suggestion and offer? For example these following sentences: Shall I turn on the light?/Shall we go to the library and look it up?
4-In prediction do we use shall,will and be going to?
5-Can we use the word control instead of exams?
6-Can we say the train is due? and what does it mean?
7-Can we use the present perfect to indicate the future?
8-By the time the test begins, I'll have forgotten everything. Why have we used the present in (begins)
Thank you in advance