When do you use will and shall?

Answer 1

Strictly speaking, will is the auxiliary verb of the future tense for the second and third persons ( you, he, she, it and they), and shall is the auxiliary for the first person ( I, we). Thus we have "You ( or he, she, it or they ) will leave Rome tomorrow and I (or we) shall arrive there then." In American usage this distinction is not generally maintained, and willis the auxiliary of the future tense for all persons.

Shall with the second or third person as in "It shall be done," and "You shall be rewarded" conveys the sense of a command or a promise. By the same token will with the first person, as in "I will not be treated this way" and "We will have peace" has the same sense.

Shall I? and shall we? normally express impatience or sarcasm, as in "Let's keep it down, shall we?" or a request for affirmation or confirmation, as in "I'll serve the coffee, shall I?"

Answer 2

Shall is an auxiliary verb it is used with other verbs. It is used to make offers and suggestions:

Shall we go out tonight? -- shall + go

Shall is also used to talk about future plans: I shall see you tomorrow. -- shall + see

Will is also an auxiliary verb and is used with other verbs to talk about the future:

I will leave later. We will get some bread when we go. -- will + get

Will is not usually used when talking about future plans.