When you describe a moment in the past in Spanish, you have to pick between fui, estuve and estaba. The choice comes down to whether something finished or kept going, and whether you are talking about movement or location.
Fui is the preterite of ir, meaning "I went". You use it when you completed a journey to somewhere: Fui al supermercado (I went to the supermarket). The action started and ended.
Estuve is the preterite of estar, meaning "I was in a place". You use it when you spent time at a location and that time is over: Estuve en la playa toda la tarde (I was at the beach all afternoon). The visit finished. A whole day at the gym is a completed block of time, so the answer is estuve.
Estaba is the imperfect form of estar. You use it to describe how things were while something else happened, or to paint the scene without a clear endpoint: Estaba en el gimnasio cuando me llamaste (I was at the gym when you called). The imperfect does not mark the end of the time.
Preterite vs imperfect: the core difference
Spanish speakers split the past into two boxes. Preterite (pretérito indefinido) is for finished actions: went, arrived, stayed, left. Imperfect (imperfecto) is for ongoing background, habits, or interrupted moments: was, used to go, felt.
If you say Estaba en el gimnasio todo el día, it sounds weird to a native because you are using imperfect for a time block that clearly ended. You finished the day at the gym. That calls for estuve.
But if you say Estaba en el gimnasio cuando llegó mi amigo, that is perfect. Your friend arrived and interrupted. The imperfect sets the scene.
Real sentences you will hear
Fui al cine ayer means I went to the cinema yesterday and the outing is done. Estuve en el cine tres horas means I was at the cinema for three hours, and those hours finished. Estaba en el cine cuando recibí tu mensaje means the cinema was where I was when your message landed.
Native speakers feel these as different stories. Fui tells you about movement. Estuve tells you about location in a closed time frame. Estaba tells you about a moment or a condition that was interrupted or backgrounded.
How to stop freezing when you speak
Memorizing rules helps, but using them in real conversation is different. You need to hear native speakers say these sentences and say them back. You need someone to correct you when you get it wrong, in the moment, while you are talking.
PBC Languages (People Building Connections) runs free language exchanges with native Spanish speakers. You match with a partner, usually for 30 minutes at a time, and you both teach each other. Your partner speaks Spanish with you, and you speak English with them. No money changes hands. These exchanges run on the principle that a language lives between people, not in an app or a textbook.
You also learn in live classes with a maximum of four students. Four is small enough that you cannot hide. You speak every class. The teachers are experienced and chosen one by one, and the first class is free so you can try it. Between classes, WhatsApp groups and cultural events keep your Spanish alive and give you reasons to use what you learned.
The point is consistency. You do not finish Spanish. You show up, you connect with real people, and you keep going. That is how you move from knowing the rule to living it.
