Shall and will have the same meaning but are used in different grammatical context. In British English, shall is used for first person and will is used for 2nd person or 3rd person.
In American English, shall is not used very often. Will is used instead, especially in its shortened form. For example, I'll see you tomorrow.
- I shall go to the movie tonight.
- We shall overcome.
- She will by happy to sign the contract.
- They will visit the mosque for evening prayers.