In everyday American English, will is the usual choice for future statements, predictions, and promises. Shall still appears in offers and suggestions with I or we and in some formal writing.
Use will for a future statement
The library will open at nine tomorrow states what is expected to happen. I’ll return the books on Friday can express a plan or a promise. I’ll is the contraction of I will here.
Will works with any subject. See Auxiliary Verb for the role of will and shall before the base form of a verb.
Use shall for a suggestion or offer
Shall we meet at the library? suggests a plan. Shall I bring the books? offers to do something. In formal speech or writing, I shall return can state an intention.
In rules and other formal documents, shall can express a requirement. In The chair shall call the meeting to order, the wording can assign the chair a duty. In ordinary instructions, must makes a requirement explicit.
