As a general rule, use 'will' for affirmative and negative sentences about the future. Use 'will' for requests too. If you want to make an offer or suggestion with I/we, use 'shall' in the question form. For very formal statements, especially to describe obligations, use 'shall'.

When we use shall with examples?

The traditional rule is that shall is used with first person pronouns (i.e. I and we) to form the future tense, while will is used with second and third person forms (i.e. you, he, she, it, they). For example: I shall be late. They will not have enough food.

When shall we or when can we?

The main difference between shall and can is the tense that is associated with. Shall is always in future tense and can is always in present tense. Shall focus on making an offer or suggestions but can focus on expressing opportunities, promising and volunteering.