You can use I’ll… (I will) when you offeror decide to do something:
My bag is very heavy.’ ‘I’ll carry it for you.’
‘I’ll phone you tomorrow, ok?’ ‘Ok, goodbye.’
We often say I think I’ll… / I don’t think I’ll… when we decide to do something:
I’m tired. I think I’ll go to bed early tonight.
It’s nice day. I think I’ll sit in the garden.
It’s raining. I don’t think I’ll go out.
Do not use the present simple (I go / I phone etc.) in sentences like these:
Do not use the I’ll… for something you decided before
I’m working tomorrow. (not ‘I’ll work’)
There’s good film on TV tonight. I’m going to watch it. (not ‘I’II watch)
What are you doing at the weekend? (not ‘ what will you do’)
shall I…? shall we…?
shall I /we…? = Do you think this is a good thing ta da? Do you think this is a good idea?
It’s very warm in this room. Shall I open the window?
‘Shall I phone you this evening?’ ‘ yes, please,’
I’m going to a party tonight. What shall I wear?
It’s a nice day. Shall we go for a walk?
Where shall we go for our holidays this years?
‘let’s go out this evening.’ ‘Ok, what time shall we meet?’
