Let's consider the preterite tense of a regular -ar verb. To determine the correct forms of a verb, we start with its infinitive form. The infinitive form of the verb meaning (to speak) in Spanish is (hablar).

Now we take off the -ar ending:
hablar - ar = habl

Now we add on one of the preterite tense endings. The ending chosen will depend upon the gender of the subject and whether it is singular or plural.