We also use had better to give advice.  "You had better …" means "It would be better if you …"
Examples:
     They had better start listening before it's too late.
     You're ill.  You had better see a doctor. (NOT You have better see a doctor.)

Had better is used to say what is the best thing to do in a particular situation.

Had better is stronger than should or ought to, although it is not as strong as must.
     I'd better tidy my room up. (= I'm going to tidy my room up, because it is the best thing to do.)

The negative is had better not.  The short form is ’d better (not).
Examples:
     She had better not do that.
     Hurry up!  You'd better not waste time. 

With had better, we normally use an indirect question rather than a direct one.
Example:
     Do you think I'd better see a doctor?