What is the Spanish present tense, when and how do you use it?

In Spanish, there are three categories of verbs. The category is determined by the last two letters of the infinitive:-ar verbs (like hablar)
-er verbs (like comer)
-ir verbs (like vivir)
The infinitive is the base form of the verb, such as to speak, to eat, to live, etc. In Spanish, all infinitives end in -ar, -er, or -ir.
To conjugate a verb means to manipulate the infinitive so that it agrees with the different possible subjects. 
These are the personal pronouns: 
Many Spanish verbs are completely regular, meaning that they follow a specific pattern of conjugation. In this lesson you will learn to conjugate regular -ar, -er, and -ir verbs (in the present tense). Before you can do that, you must memorize the following subject pronouns.
yo (I)
tú (you – informal)
él (he)
ella (she)
usted (you – formal)

nosotros/nosotras (we)
vosotros/vosotras (you-all – informal)
ellos/ellas (they)
ustedes (you-all formal)
Spanish infinitives are divided into two parts: the ending and the stem. The ending is the last two letters. The stem is thus everything that’s left after you remove the ending.
habl + ar = hablar
com + er = comer
viv + ir = vivir
You remove the ending of the infitive and add the ending of the present tense to conjusgate the verb. 
AR: o as a amos ais an
ER: o es e emos eis en 
IR: o es e imos is en