Conjugated Verb or Infinitive?

The Spanish infinitive (a verb ending in -ar, -er, or -ir) is often used after a conjugated verb (a verb that is changed to reflect the subject and time.) Example:
Yo quiero bailar. / Quiero bailar. (I want to dance.)
Quiero is a conjugated verb. It goes with the subject is "yo" and the time is the simple present. Bailar is an infinitive verb. It ends with -ar.

Do not use the infinitive for the main verb that goes with the subject of the sentence. Conjugate it to match the subject. Example:
Yo bailo con mi amigo. (I dance with my friend.)
Here, the verb "bailo" goes with the subject "yo." It cannot be in the infinitive form (bailar) in this sentence.