Shall is a modal verb in English with multiple uses:
1. To express future tense in formal contexts: "I shall return tomorrow."
2. To indicate obligation or requirement, especially in legal documents: "The tenant shall pay rent on the first day of each month."
3. To make suggestions or offers: "Shall we go for a walk?"
4. In questions to ask for advice or instructions: "What shall I do with this package?"
5. In older English, to express determination or command: "You shall not pass!"