What is the difference between 'shall' and 'will'?

Will and shall, both imply a command. "You will or shall wash the dishes." It is up to the person issuing the command which to use and the person to whom the command is given is expected to comply. May and could, imply permission or suggestion. "You may or could wash the dishes." It implies that it is up to the person receiving the request whether to comply or not.