This is a rather tricky topic, so I will explain it in English.
What is a verb? ¿Qué es un verbo?
A verb is what carries the meaning of the sentence from point A (the subject) to point B (the complements).
Take this sentence: "I ... chocolate"
What is the meaning? We don't know, because the sentence is incomplete: the verb is missing. We could guess: I like chocolate, I love chocolate, I hate chocolate, I eat chocolate, I ate chocolate, I buy chocolate...
Let's add a verb: "I eat chocolate"
Now it makes sense, because there is a verb ("eat") bringing the meaning from "I" to "chocolate".
In this way, we can compare the verb with a car. The car's function is to bring us from A to B. The verb's function is to bring the meaning from the subject ("I") to the complement ("chocolate").
Just like a car, a verb can be on or off.
When it is on, the car is in movement. We know it is on, because there is a driver (the subject) at the wheel. The verb is on when it is conjugated in a tense: "I eat" (present tense), "I ate" (past tense), "I will eat" (future tense).
When it is off, the car is parked. There is no driver. The verb is off when it is not conjugated: we call this the infinitive form. In English, we know a verb is in the infinitive form because it is preceded by the word "to": "to eat". In Spanish, we know the verb is infinitive (infinitivo) when it ends in AR, ER or IR.
Llamar (to call)
Comer (to eat)
Vivir (to live)
Note: Sometimes, you may encounter verbs ending in ARSE, ERSE or IRSE. These are reflexive verbs and the "SE" bit is a reflexive pronoun attached to the verb (just like a trailer is attached to a car).
Llamarse (to call oneself)