Quick explanation:
A verb is the action in the sentence.¹ An infinitive is the simplest form of the verb. An infinitive ends in “r” and usually means: “to ____”.

hablar - to talk
correr - to run
salir - to go out, to depart

Long explanation:
Defining the terms:
We should explain some terms you might see in this lesson or similar lessons.

A verb is usually the action in the sentence.¹

When we conjugate a verb, we change the verb ending, depending on the person we are referring to.

(yo) como. → (él) come
   I eat → he eats

Conjugated verbs:
Here are some examples of conjugated (changed) verbs. Notice how the endings of the verb are different for different people.

El caballo come la zanahoria.
   The horse eats the carrot.
(Nosotros) Corremos con el perro.
   We run with the dog.
Ellos hablan a la vez.
   They talk at the same time.

Infinitive:
Unlike the verbs above, the infinitive form of the verb ends in "r". It is the simplest form of the verb. It usually means “to ___”.
 ex:
   ser (to be)
   bailar (to dance)
   comer (to eat)
   dormir (to sleep)
   poder (can / to be able)
   cantar (to sing)
   morir (to die)
   escribir (to write)
   comprender (to understand)

There are three types of infinitive verbs:

-ar verbs → hablar
-er verbs → comer
-ir verbs → escribir

Uses of the infinitive:
The infinitive is used in the following situations.

1. directly after another verb
• María necesita estudiar.
     Mary needs to study.
• (Yo) Necesito leer un libro.
     I need to read a book.
• Quiero ser médico.
     I would like to be a doctor.
• Vamos a jugar al béisbol.
     We’re going to play baseball.
• Los estudiantes tienen que estudiar para el examen mañana.
     The students have to study for the test tomorrow.
• A los hermanos de Julia les gusta mandar mensajes de texto.
     Julia’s brothers like sending text messages.

2. after prepositions: a, de,² para, & por
• Antes de ir a la piscina, Juan y Gabriela tienen que limpiar sus cuartos.
     Before going to the pool, Juan and Gabriela have to clean their rooms.
• Fuimos a comer después de salir del concierto.
     We went to eat after leaving the concert.
• Mis primos van al parque para conseguir novias.
     My cousins go to the park [in order] to get girlfriends.
• Por hablar con otro muchacho, su novio se enojó con ella.
     Because of her talking with another boy, her boyfriend got angry with her.

3. as a noun
• Correr es bueno para la salud.³
     Running is good for your help.
• No es buena idea tomar muchos refrescos de energía.
     It’s not a good idea to drink a lot of energy drinks.
• Las investigaciones afirman que dormir entre 7 y 9 horas cada noche es bueno.
     Studies show that sleeping between 7 and 9 hours each night is good.
• El caminar humano nació hace 4 millones de años.⁴
     The human race was born 4 million years ago.
• Para mí, el bailar es algo sublime.
     In my opinion, dancing is something wonderful.