Dgeigh, this may help a speck, though for me parts of it raise more questions:
'DO', 'BE' and 'HAVE' are the English auxiliary verbs used in a negative structure, a question or to show tense. ...
3/ 'HAVE' is used with the Past Participle to form the Perfect Aspect
Under Perfect Aspect, it has:
The perfect aspect is formed with the auxiliary verb 'to have' + the past participle. It is used for finished actions that are relevant to the time referred to or ones that continue up to the time referred to:

She's worked here for donkey's years. (this continues up to now)

I've lost my keys. (a past action that is relevant now as I can't open the door) From:
http://www.usingenglish.com/glossary/auxiliary-verb.html

I was pleased that one of the sites I looked at called aux. verbs helping verbs; that is the term I was taught but couldn't remember.