1) The document discusses modal verbs and their meanings and rules of use in English. 2) Modal verbs such as can, may, must, should are used to express ideas like ability, obligation, permission, prohibition, advice, necessity, possibility and probability. 3) Modal verbs are special in that they don't take an 's' in the third person singular and are followed by an infinitive without 'to'. They also don't require an auxiliary verb in negative or interrogative sentences.

2. Modal verbs - meanings Meaning Modal verb ability can Obligation/duty Must / have to, has to permission may, can prohibition mustn’t advice Should /shouldn’t Not necessary Don’t have to /does’nt have to probability may, might, can possibility can