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.
I will not tolerate such behaviour.
You shall go to the ball!
In practice, though, the two words are used more or less interchangeably, and this is now an acceptable part of standard British and American English; however, the word shall is now seldom used in any normal context in American English.