The Präteritum is used mainly in formal writing and you will have to remember only a very few forms of it for now as you are most likely not going to write a novel in German anytime soon. I will explain the precise differences between Perfekt and Präteritum at the later in this course, so don‘t worry about it for now. For those who are impatient: there is none. You always use the Perfekt. More details as promised later.
The regular form of the Präteritum is pretty simple. Take a look at these examples and try to figure out what they have in common:
es machte
es sagte
es kochte
So all you‘ve got to do is to take the stem of the infinitive and add a -te- but hold back another second. Of course there are still the personal endings to be considered:
ich machte.*
du machte.st
es machte.*
wir machte.n
ihr machte.t
sie machte.n
That‘s mainly it for the regular forms. Maybe it‘s interesting to note that separable verbs behave „normally“ in the Präteritum:
Er machte.* das Licht an.
Als er das Licht anmachte.*.
*In the regular Präteritum the ich and es-forms do not get a personal ending. They are always (!) identical, just like the wir and the sie- forms.
This topic is covered in: B1-L08