El verbo - At the beginning was the verb

Verbs are the switchgboards of the sentences. The kind of verb you use pre-determines the choice and number of the other words in the sentence. When you use a verb in a sentence, generally you have to conjugate it, the same as in English, even though the conjugation system in English is much simpler than in Spanish.
 

I go	Yo voy
You go	Tú vas
He/ She/  goes	El/ Ella/ Ud. va
We go	Nosotros/as vamos
You go	Vosotros/ as vais
They go	Ellos/ Ellas/ Uds. van

As you can see, the verbs agree with the subjects (the one who does something). Because we have different verb forms for each person, Spanish speakers very often omit the personal subject pronoun. It is only used to clarify, focus, contrast and emphazise whoor what the subject is.

Normalmente ___ tengo clases a las nueve. Mi amiga Ana tiene todas sus clases en la tarde. Por eso ella no se levanta antes de las 11 de la mañana. (We have two subjects in these sentences, Yo and Ana. Even though the ending of 'levanta' indicates that I am refering to Ana and not to myself, I have used the pronoun ella, to clarify and emphazise that I am talking about Ana and not about myself.

Most often you will encounter the pronouns of the third person, because as you can see in the table above, we have only one ending but three different persons.

Ella es profesora, él es ingeniero y Ud. es secretaria en una oficina.

But even in sentences with different subjects in the third person, the use of the pronoun might be unnecessary if the context makes clear who or what we are talking about in the different contexts.

A verb consists of a stem and and ending:
 
 

hablar	habl + ar	stem + ending
comer	com + er	stem + ending
vivir	viv + ir	stem + ending

Apart from the the person, we can also see at the verb form the tense (past, present, future) and the mood (conditional, subjunctif) of the sentence.

We have different verb conjugations (endings and sometimes different stem changes) for each different tense and mode in Spanish.
The tenses in Spanish are:
 
 

English Terminology	Our Terminology	Spanish Terminology
Present Preterite Imperfect Present Perfect Pluperfect/ Past Perfect Future	Presente Pretérito Imperfecto Presente Perfecto Pluscuamperfecto Futuro	Presente Pretérito Indefinido Pretérito Imperfecto Pretérito Perfecto Pretérito Pluscuamperfecto Futuro