a) Do we use will /won't to talk about present, past or future?

We use will /won't to talk about future.

b) Do we use will /won't to talk about planned or not planned things?

We use will /won't to talk about not planned things.

c) What is the full form of won't?

The full form of won't is will not.

d) What form of the verb do we use after the verb will?

After the verb will we use the infinitive form of the verb.