You use not with verbs to form negative statements.

You use not to form questions to which you expect the answer 'yes'.

You use not, usually in the form n't, in questions which imply that someone should have done something, or to express surprise that something is not the case.

You use not, usually in the form n't, in question tags after a positive statement.

You use not, usually in the form n't, in polite suggestions.

You use not to represent the negative of a word, group, or clause that has just been used.

You can use not in front of 'all' or 'every' when you want to say something that applies only to some members of the group that you are talking about.

If something is not always the case, you mean that sometimes it is the case and sometimes it is not.

You can use not or not even in front of 'a' or 'one' to emphasize that there is none at all of what is being mentioned.

You can use not in front of a word referring to a distance, length of time, or other amount to say that the actual distance, time, or amount is less than the one mentioned.

You use not when you are contrasting something that is true with something that is untrue. You use this especially to indicate that people might think that the untrue statement is true.

You use not in expressions such as 'not only', 'not just', and 'not simply' to emphasize that something is true, but it is not the whole truth.

You use not that to introduce a negative clause that contradicts something that the previous statement implies.

Not at all is an emphatic way of saying 'No' or of agreeing that the answer to a question is 'No'.

Not at all is a polite way of acknowledging a person's thanks.