This is a pretty huge question. I guess you're talking about auxiliary (helping) verbs. I'll try to be brief...
For "have", it's used in present perfect: have been, have eaten, have forgotten, have talked... the other verb must be the past participle form. You use this when you describe a present situation using a past event (eg. the reason for the present situation).
You'll also see it as an obligation "have to (verb)", or in speech as possession "have got (something)".
"Can" is a modal, and needs another verb in base form to follow: can be, can eat, can forget, can talk... you use this to indicate ability.
"Be" is used to follow modals such as can, or used after "to" as the infinitive form. You'll also see it used subjunctively, but not so often.