In all of the provided sentences, "fui" means "I was."
- Fui al médico - "I went to the doctor."
- Fui a Madrid - "I went to Madrid."
- Fui estudiante - "I was a student."
- Fui ayer - "I was yesterday."
However, "fui" translates to "I went" in the first two sentences due to the verb "ir" (to go). The third sentence translates "fui" as "I was," and the fourth could imply a past action with "yesterday."
The best example where "fui" clearly means "I was" is:
- Fui estudiante.
This is the clearest instance of "fui" meaning "I was."