What's the difference between will and shall?

Formerly, shall was used as the first person form of the verb will to express future tense. Using will in first person implied intent or definite decision. When shall was used in second or third person, it expressed obligation.

In modern American English, shall has generally been replaced by will. Shall is reserved mainly for contexts in which the speaker wants to sound formal or extremely polite.

However, when shall and will introduce questions, they have an important distinction in meaning. Shall asks for a preference or offers a polite suggestion, while will indicates future tense.

"Shall we get a cup of coffee?" means "Do you want to get a cup of coffee?"
"Will we get a cup of coffee?" involves speculation about future events, such as: "Do they serve coffee at this restaurant?" or "Is coffee included in the price of the meal?"