A. There are various modal auxiliary verbs, many falling into pairs, e.g. can/could, may/might, shall/should, will/would, must, ought to and dare.
B. The meanings they express are complex and depend upon the context of their use. For example, ‘I can/could go on Saturday’ (strong/weak possibility), auxiliaries tend to differ from typical English uses.
C. The meanings expressed by some modal auxiliary verbs are similar to those expressed by adverbs such as ‘maybe’, ‘certainly’ ‘possibly’ and so on. Sometimes both modal auxiliary verb and an appropriate adverb are used together in a sentence, e.g. ‘You could maybe help me to paint the guest room this weekend?’