All Spanish verbs end in either -ar, -er or -ir. This form of the verb is called the infinitive. For example:
The infinitive is the form of the verb you will find in a dictionary.
However, the infinitive doesn't tell us the person of the verb (ie who is doing the action) or the tense of the verb (ie when the action takes place / took place / will take place, etc). To do this you need to conjugate the verb (ie change it into a different form).
To work out how to conjugate a verb correctly, ask yourself: