There are two common uses for the Tagalog word na

na, adv
now, already

This Tagalog word is used more often than 'now' and 'already' in English. It's in almost every other Tagalog sentence that's uttered in conversation.  

Tapos na ako.
I'm finished now.
(In English you could simply say, "I'm done.")


Kumain ako.
I ate.

Kumain na ako.
I've eaten (already).

Mag-aral ka.
Study. (telling you to study)

Mag-aral ka na.
Study already.(telling you that it's time to study)

Pasko na. Maghanda na tayo.
It's Christmas already. Let's get ready already.

Martes na. Magtrabaho na tayo.
It's Tuesday already. Let's work already.

Another use of the word na is to connect a noun and whatever is describing it. 

bahay na malaki
a house that's big
= malaking bahay (a big house)

prutas na hinog
a fruit that's ripe
= hinog na prutas (a ripe fruit)

matapang na babae
a woman that's brave
= babaeng matapang (a brave woman)