Japanese verbs mostly fall into three conjugation categories, besides a small number of irregular verbs. These three categories are called ichidan verbs, godan verbs, and suru verbs.
Ichidan (一段いちだん) verbs, also known as -ru verbs, always end in either -iru or -eru. The final る drops in many conjugations. Models:
Godan (五段ごだん) verbs, also known as -u verbs, can end in any of the following letters: う・く・ぐ・す・つ・ぬ・ぶ・む・る. These verbs have different sound changes in the past tense and -te form depending on their final letter, and they are grouped according to this into different verb models for each possible final letter. Models:
Suru (する) verbs end in the auxiliary verb する “do”, often formed by adding する after a noun to turn it into a verb, such as 勉べん強きょう “study (noun)”, 勉べん強きょうする “study (verb)”. Models:
There are a handful of verbs in Japanese with irregular conjugations that do not fit into the previous categories. Models: