This phrase is used in Spanish to indicate the time and usually followed by a place or context, like:
* Es la una en la tarde. (It is one o'clock in the afternoon.)
* Es la una en la mañana. (It is one o'clock in the morning.)
* Es la una en el restaurante. (It is one o'clock in the restaurant.)
Let me know if you have any other Spanish phrases you'd like me to explain!