An aspect of English that troubles many learners is the correct use of the modal verbs - must, may, can, should, ought to, might etc. The difficulties are of two kinds - firstly, there is the difficulty of learning which forms of the modal verbs are possible in the various tenses, and secondly, there is the more subtle difficulty of choosing the correct modal to express the meaning that you want to convey.
As a taster to some of the difficulties you will find on the pages listed below, consider the following question:
The statement You might have told me, when read rather than heard, is ambiguous. Which two meanings does the sentence have, and how would the sentences be spoken so that the listener would have no difficulty understanding what you meant?
You might have told me can mean either It is possible that you told me (but I don't remember). Or it can mean Why didn't you tell me? - for example, You might have told me that she's divorced. I felt such a fool when I asked where her husband was! With the first meaning, the word might is usually stressed and the rest of the sentence is spoken with falling pitch. With the second meaning, each of the words in the statement receive equal stress and the pitch remains on the same level.
In fact, there is a way that the meaning could be determined from the written words alone. Of course, the context would usually be enough to know what the writer wants to say, but in addition to this, the sentence having the second meaning would probably end with an exclamation mark. You might have told me!