A lot of students have been confused by older textbooks which refer to 'will' as 'the future tense'.
A key factor to remember about 'will' is that when we talk about the future we cannot always use 'will' and that when we use 'will' we are not always talking about the future.
In these examples 'will' is clearly referring to the future.
I'll probably visit Sue Kay when I go to Oxford.
If I see her, I'll tell her about it.
Next year she'll be 42. Or so she says.
However, in these examples 'will' is referring to events happening at the present.
When we use 'will' referring to the present, the idea being expressed is usually one of 'showing willingness' or 'will power'.
My baby won't stop crying. I've tried everything and I'm really exhausted.
I am the boss. You will do as I say.
I need quiet to write this but he will keep on talking to me. I wish he would leave me alone.
Use 'will' for requests, orders, invitations and offers.
Use 'will' for promises and threats.
Use 'will' for insistence.
Use 'will' for habit.
Use 'will' for deduction.
Look again at all of these examples of 'will'. They are all to do with the present or are 'timeless'.