The verb

A فِعْل (fi'l) is a word that describes an action — and it never describes one without also fixing it in time: past, present or future. That is the whole difference between a verb and an ism. An ism means something; a verb means something and tells you when.

An Arabic verb is never only the action. Packed inside the same word is a ضَمِير (ḍamīr) — a pronoun — telling you who did it: the person, the gender and the number of the one carrying out the action.

So نَصَرْتُ (naṣartu) is two pieces of information in one word.

English needs two words where Arabic needs one. This is why an Arabic verb can be a whole sentence by itself.

This section settles two questions — when the action happened, which is Tense, and whether the doer is named, which is Voice.