Six useful french phrases for every day use that everyone should know, but are somehow are not taught in schools:

1. Ça roule? -Comme d’hab!

"Ça roule" is an expression that has become almost parasitic; the French use it (and its variations like "Ça marche", "Ça va") at least once every thirty minutes. This phrase is used when people want to ask/say "things are going OK", life is treating them well, no major problems are expected, and the speaker is generally doing all right.

2. Peu importe!

This is an expression of indifference, meaning that you don't mind either of the proposed options. In English, its equivalent is "whatever".

3. C’est n’importe quoi!

This is a similar phrase with a completely different emotional colouring. It is like "oh my God", "that's crazy!", "this is totally insane!". It is used when someone does something stupid or illogical.
For example: Le president a bien fait d’augmenter les impôts. C’est n’importe quoi!

4. Laisse tomber...

The literal translation is similar to the English equivalent "leave it" when you want to weaken the significance of the statement, in other words, "laisse tomber" may be equivalent to "forget it."
For example:
-Et alors? Est-ce que tu as eu ton augmentation de salaire ?
-Laisse tomber…L’entreprise a fait faillite!

5. Bref

We have a similar parasite word: "in short".  So "Bref" is its French equivalent. You use it when you want to reduce the story to a minimum and convey only the very essence of it. However, the word "Bref" has somewhat more literary meaning: it also means "in general".
For example: Elle m’a appelé hier et m’a dit qu’elle n’avait pas les mêmes sentiments pour moi, et qu’au final, elle veut qu’on reste amis. Bref, elle m’a largué.

6. Tu t’en sors?

If you are asked this question by your classmate, you can probably ask him for help. When translated, this expression means "Are you getting on OK?". The French can ask "Ça marche?" to mean the same thing. (see para. 1).