What is an infinitive?
An infinitive is the basic verb form.
In English, the infinitive verb is a verb form which begins with the word 'to'. For example:  to speak, to eat, to live. In Spanish, the infinitive verb is a verb form which ends with the letters -ar, -er, or -ir. For example: hablar, comer, vivir.

Singular & Plural Subjects
Generally the subject isn't necessary because the conjugated verb indicates the subject. The subject is sometimes used for emphasis.

Singular:
1st person (I): yo
2nd person (you): tú/vos*
3rd person (you/he/she): usted/él/ella

Plural:
1st person (us): nosotros
2nd person (you guys): ustedes
3rd person (them): ellos/ellas

Verbs: Verbos
To learn more about verb tenses & conjugations Click Here >