Say “if” or “when”, depending on context.
The rule
Short past form + ら. たら can express a condition or the fact that a first action is performed before the next one.
Examples
雨が降ったら、家にいます。
If it rains, I'll stay home.
仕事が終わったら、帰ります。
When the work is done, I'll be back.
Remember
- Neutral past shape + ら: 食べたら、行ったら、静かだったら.
- たら can express a condition or "once".
In everyday life
雨が降ったら、行きません。
If it rains, I won't.
家に帰ったら、電話します。
I'll call once I get home.
Common mistake
たら is not reserved for events already past, despite its construction in た.