Start with the hours you need
The numbers one through twelve are uno, dos, tres, cuatro, cinco, seis, siete, ocho, nueve, diez, once, and doce. Connect a number to an actual clock display instead of treating the list as the whole task.
Distinguish the clock from an appointment
“Es la una” means it is one o’clock. “Son las dos” means it is two o’clock. “Son las tres y media” describes 3:30. To say that something happens at three, use “a las tres.” In a real arrangement, make the part of the day clear when it would otherwise be ambiguous.
Common misunderstanding: every hour uses the plural
One o’clock uses the singular pattern “es la una”; the other hours use “son las.” “Media” in a time expression represents half an hour. Understanding that quantity supports the language, but knowing fractions does not by itself teach the Spanish expression.
Worked example
Read a short arrangement
“Nos vemos a las tres y media de la tarde” means “See you at half past three in the afternoon.” The phrase “a las” introduces the arranged time. The final words make the afternoon context explicit.