What is "Plusquamperfekt" and how is it different from "Perfekt" ?

The Plusquamperfekt is a very special and difficult form but might be comparable with the "past perfect" tense.
One uses this tense when talking about two events in the past. Let´s say one happened this morning at 8 (event 1) and one happened this morning at 10 (event 2).
If you start by talking about event 2 first and then want to refer to event 1 you would need to use Plusquamperfekt. (Drawing a timeline) Similar to "Perfekt" the "Plusquamperfekt" needs an auxiliary and a verb (basically two verbs). We would use the past tense forms of haben and sein and the past tense of the verb. An example: Ich schlief ein, nachdem ich die Hausaufgaben gemacht hatte. Bevor sie zum Fußballtraining ging, hatte sie schon gelernt.