Preterite

Regular preterites carry mandatory written accents on the yo and third-singular forms, and dropping one turns hablé into the subjunctive hable. The big irregular group does the opposite: tuve, pude, hice, vine, puse, quise take no written accent at all. The missing accent is the marker that you are in that group.

Regular -ar verbs end in -é and -ó in the yo and él forms, -er and -ir verbs in -í and -ió: hablé, habló, comí, comió. The accent is compulsory because it changes the word: hablo is 'I speak' and hable is a subjunctive. Verbs in -car, -gar and -zar change the yo spelling: busqué, llegué, empecé.

Ser and ir share one preterite: fui, fuiste, fue, fuimos, fuisteis, fueron. Context tells you which: fui al cine is 'I went to the cinema', fue mi profesor is 'he was my teacher'. Dar and ver are short too, and one-syllable forms take no accent: di, dio, vi, vio.