You learn the dictionary form (辞書形) of Japanese verbs (instead of common, polite ます form). Because from dictionary form, it is easiest to derive into other forms (conjugate). You can search the dictionary form at OJAD.
I’ve spent time figuring the best way to understand the rules and types of verbs, but they are not useful with many exceptions. That’s not how Japanese people learn in school. My approach is to get enough exposures! Forget all the formulas.
The most impactful verbs you can study are する and 来る! These two are useful and has no exceptions.
For the rest of verbs, you just see them enough times til you remember. Let me give some examples:
The past tense of 倒れる, fall down.
男性が自宅で倒れていた / A man fall down in his house
There are unlimited verbs by adding する to the end of noun:
The past tense of 救助する (尊敬), rescued.
警察に救助された / Rescued by Police
与え, 与える, give
警官は男性に食べ物を与え / Police gave food to the man
Hope this helps!
Verbs I frequently see being used: