French has a whole layer of familier vocabulary. It's what friends use, and you'll hear it constantly — but it changes your tone, so know which word you're choosing:

Familier	Standard	English
bosser	travailler	to work
le boulot	le travail	work, job
un truc	une chose	a thing, a whatsit
un pote	un ami	a mate
un mec	un homme	a guy, a bloke
la bouffe	la nourriture	grub, food
une bagnole	une voiture	a car
le fric	l'argent	cash, dosh
crevé(e)	très fatigué(e)	knackered
kiffer	adorer	to love, be into

Copain / copine sits in between: a friend — or a boyfriend or girlfriend, depending on context. Mon copain can mean either.