What time is it?

Es la una and Son las dos have the literal translations of 'It is the one' and 'They are the two'.

The first of these Es la una is singular which is why la as opposed to las is used.

The basic grammar contains more explanations about gender in Spanish.

English	Spanish	Audio
What time is it?	¿Qué hora es?
It is 1 o'clock	Es la una
It is 2 o'clock	Son las dos
It is 3 o'clock	Son las tres
It is 4 o'clock	Son las cuatro
It is 5 o'clock	Son las cinco
It is 6 o'clock	Son las seis
It is 7 o'clock	Son las siete
It is 8 o'clock	Son las ocho
It is 9 o'clock	Son las nueve
It is 10 o'clock	Son las diez
It is 11 o'clock	Son las once
It is 12 o'clock	Son las doce

More example Spanish phrases illustrating how to tell the time in more detail.

To say 'quarter past' and 'half past' the hour in Spanish, add y cuarto 'quarter past' or y media 'half past' to the basic time phrases above.

To say 'quarter to' the hour, add menos cuarto to the basic phrases.

English	Spanish
It is half past one?	Es la una y media
It is half past two?	Son las dos y media
It is quarter past three?	Son las tres y cuarto
It is quarter past four?	Son las cuatro y cuarto
It is quarter to eleven	Son las once menos cuarto
It is five minutes past one?	Es la una y cinco

If you have already learnt the Spanish numbers up to 12, the time expressions will be easy.