What are examples of modals and give their functions?

Modals are auxiliary verbs that express necessity, possibility, permission, or ability. Examples include "can" (ability), "must" (necessity), "may" (permission or possibility), and "should" (advice). Each modal modifies the main verb to convey different shades of meaning, such as obligation or likelihood. For instance, "You must finish your homework" indicates a strong obligation, while "You may leave early" grants permission.