We use will (+ base verb) when we decide to do something at the time of speaking.
eg. I forgot my bag in the classroom. I’ll go and take it.
The negative form is will not (won’t).
Will can also be used in these situations:
- offering to do something: You live far away from school. I’ll give you a lift.
- agreeing to do something: Can you finish the report for me? OK, I’ll do it.
- promising to do something: Thank you for sharing your secret with me. I promise I won’t tell anyone.
- asking somebody to do something: Will you please close the door? It’s a bit cold.
Shall is mostly used in the questions Shall I…? / Shall we…?
We use shall to ask for somebody’s opinion: Shall I buy that dress?
Shall is only used with I and We (first person singular and plural)