This is a practical summary of the main meanings expressed by the set of verbs generally called modal verbs or modals.
Modals can express a varied range of ideas and shades of meaning, very useful to complete the English verb conjugation system.
They are usually divided into central modals(can/could, may/might, must, shall/should, will/would) and semimodals or marginal modals (ought to, used to, need, dare).
I'll concentrate on the main meanings expressed by the central modals, though I will include some notes about the following semi-modals: ought to, as an alternative to should,needn't (the negative of need), for absence of obligation, and used to, for habitual actions in the past, as against to be used to, for sth you are accustomed to doing.