In English the past tense is formed by adding -ed to regular verbs, so that "I talk" becomes "I talked." In Spanish the preterite tense is formed by adding a specific ending to each verb, different than the present tense (except for the nosotros form that stays the same).
The preterite = the past tense
Hablar = to talk
Hablé = I talked hablamos = we talked
Hablaste = you talked hablasteis = you all talked
Habló = He talked hablaron = they talked
Last year you learned how to talk about the past tense, by using "acabar de" + an inifintive verb:
Acabar de + infinitive verb = to have just done something
Yo acabo de comer. = I just ate.
Irregular preterite verbs:
There are many irregular forms for the preterite. We learned about car/gar/zar verbs when forming the negative tú command, The same rule applies for the preterite of the yo form.
Tocar = to play Command form tú
toqué tocamos Toca No toques
Llegar = to arrive
Llegué llegamos Llega No llegues
Cruzar = to cross
crucé cruzamos Cruza No cruces