Ser, is one of two Spanish verbs meaning 'to be' and learning how to conjugate ser
in the preterite tense is usually quite tricky for most students because it follows a very irregular pattern of conjugation.
However, there is also one other thing that should be noted and that is - not only is the preterite conjugation of ser highly irregular it also shares it's exact conjugation with another verb, the Spanish verb ir, which is the Spanish verb meaning 'to go', and an explanation of this will follow the actual conjugation below along with some working examples.
Ser 'to be' (conjugated in the preterite past tense)
yo fui - I was
t fuiste you was
l fue - he was
ella fue she was
nosotros/as fuimos we were
vosotros/as fuisteis you were
ellos/ellas fueron they were
As explained above ser and ir are conjugated exactly the same in the preterite and the only way you can tell whether someone is saying 'was' or 'went' is by how it used, or rather the context in which the verb is used.
For example:
El fue un buen hombre which translates into, 'he was a good man'.
El fue al supermercado which means, 'he went to the supermarket'.
Even though both examples begin 'el fue' it becomes apparently clear from the rest of each sentence which verb is being used.
In case you need them, here are a few pointers as to when one should use the preterite past tense. It should be used;
to express single past events that have been completed
to express actions that were repeated a certain number of times
to express an action that happened during a specific period of time
to express an action that was part of a chain of events