It tells that someone does something, did something or is about to do something. A verb has two distinct properties, first of all it has a special tense, an indication of time, it tells whether something happens now, in the future or in the past. Besides the tense, a verb also has a specific conjugation, the verb has to put in a sentence in such a way that it agrees with the person that is saying it. In English conjugating verbs is pretty easy but in most foreign languages it's a lot more difficult. There are also two types of verbs, there are those who are follow a specific set of rules, the regular verbs, and there are those which appear to be constructed at random and therefore have to be memorized, the irregular verbs.
Most verbs are regular verbs and that's of course the easiest kind.
We'll now go through all the tenses that exist. We already mentioned that a tense is an indication of time, it tells when the action occurs. The present tense - the easiest and most standard one, it indicates that it the action occurs right now. The past tense - a very common tense to express that something happened in the past. The perfect tense - a tense that expresses that already HAS happened.