Germanic languages* divide their verbs into two main groups, weak and strong.
Weak verbs aren't very weird, they work pretty much like regular verbs in Romance languages, where you add different suffixes to the stem depending on the tense and person. Or well, Norwegian, Swedish and Danish don't conjugate verbs for person, but all others do as far as I know. Bokmål is simpler than all the other North-Germanic standards since it doesn't divide its weak verbs further into sub groups and instead the preterite and perfect/pluperfect form is decided purely by what sound the stem ends in.
Of course, this being Norwegian there is some flexibility and the exact pattern may shift a bit depending on what register you use, but it's no different than being able to chose the number of genders or the definite plural forms for neuter nouns.
Strong verbs are a little different, they use suffixes too but not the exact same ones as the weak ones, and they combine them with something called ablaut
, that is that the vowel in the stem changes according to rules that go all the way back to Proto Indo European. Since the modern Germanic languages don't look much like their distant ancestor, you pretty much have to memorize those vowel changes for each verb by heart. Still, since they do follow some sort of pattern, it's not as difficult as if it had all been completely random and you usually develop a feel for it sooner or later
* English does and doesn't, usually students of that language learn its strong verb as simply irregular and they're lumped together with the irregular weak ones. But in all other Germanic languages it's much more productive to separate the strong verbs from the truly irregular ones.
read fluently, understand well, speak badly;
read fluently, understand badly, can't speak;
read some, understand a bit, speak a few sentences;
heritage language, want to understand and speak but can't.