I've got a test tomorrow and I have to learn the list of "Tempus praeteritum". The problem is, that I don't know what it means and where it's used for. Can anybody help me?
So first, a point of terminology. In Latin, there are two tenses* which can be called the tempus præteritum. I'm assuming you mean the third principal part of your verb (amāvī or habuī or cucurrī or audīvī), also called the simple past tense, aorist tense, or perfect tense. Out of all these names, perfect seems by far the most common, and it's the one I learned in school. So I'll use that name here.
Latin has a number of "past tenses", but the perfect is the simplest. It's the one you'd use to say "I went to the store" or "I saw the Pantheon". Often it doesn't imply anything except that the action happened in the past. So the easiest way to translate it into English is to use the simple past tense, loved, held, hurried, listened. You can also add a did for emphasis: I did say that!
When contrasted with the imperfect (the one with -ba- before the ending, like amābat), the perfect has one other meaning. It states that the action is finished, or that it was an instantaneous thing; either way, it isn't still happening. One way to translate this distinction is the simple past vs progressive past in English: perfect would be the army fought, imperfect would be the army was fighting.
Hopefully that helps. I may have misunderstood the question; are you asking for Latin → English help, or English → Latin?
*(the other being the pluperfect / tempus plusquamperfectus, but I've only seen that called the "preterite" once and it doesn't correspond as well with the English and German preterites.)