The verbs "ser" and "ir" in the simple past (preterite) have the same conjugation. Here is an explanation of each with examples:
Verb "ser" in the simple past:
Conjugation:
Yo fui (I was)
Tú fuiste (You were)
Él/Ella/Usted fue (He/She/You (formal) was)
Nosotros/Nosotras fuimos (We were)
Vosotros/Vosotras fuisteis (You all were)
Ellos/Ellas/Ustedes fueron (They/You all were)
Examples:
Yo fui estudiante en esa universidad. (I was a student at that university.)
Ella fue muy amable conmigo. (She was very kind to me.)
Nosotros fuimos los ganadores del concurso. (We were the winners of the contest.)
Verb "ir" in the simple past:
Conjugation:
Yo fui (I went)
Tú fuiste (You went)
Él/Ella/Usted fue (He/She/You (formal) went)
Nosotros/Nosotras fuimos (We went)
Vosotros/Vosotras fuisteis (You all went)
Ellos/Ellas/Ustedes fueron (They/You all went)
Examples:
Yo fui al cine ayer. (I went to the cinema yesterday.)
Tú fuiste a la tienda por la mañana. (You went to the store in the morning.)
Ellos fueron de vacaciones a la playa. (They went on vacation to the beach.)
Although the conjugation is the same, the context of the sentence tells us whether "ser" or "ir" is being used.