The passé simple is a literary past tense — it appears in novels, formal historical writing, and fairy tales, but it's essentially never used in speech or everyday writing, where the passé composé takes its place. Learners mainly need to recognize it, not produce it. Regular -er verbs form it with -ai, -as, -a, -âmes, -âtes, -èrent: il parla (he spoke).
Regular -ir and -re verbs use -is, -is, -it, -îmes, -îtes, -irent: il finit, elle vendit. Many common irregular verbs have their own passé simple stem that has to be recognized on sight: il fut (from être), il eut (from avoir), il fit (from faire), il vint (from venir). Seeing il alla or elle dit in a story is simply that verb's passé simple, playing the same role a passé composé would in conversation.