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.
There are exceptions, but this "rule" applies in most cases and in all cases in Spanish I.
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.