"car" is the shorter way to say "parce que" (because). Il est très utilisé.

French in France say "un car" when they mean a bus.

As Jmat said, the English noun "coach" refers to different things: A coach can be a large, horse-drawn, four-wheeled carriage, but it may also refer to a public motorbus (this is British English), or also to a person who trains an athlete or a singer... In France, the noun "car" refers to a public motorbus. We usually distinguish between a short-distance bus (inside the city), which we call "un bus", and a long-distance intercity bus, which we call "un car" (intercity coach service, in British English). Hope this helps! :)

Car est très exactement une conjonction de coordination (a word called conjonction serving to coordinate sentences, so, as said Araceli who is quite good with French, C2, it's very used), and you can learn toutes les conjonctions de coordination par une phrase mnémotechnique "Mais où est donc Ornicar ?" (mais -but, pero, ma, mas-, où -where, dónde, dove, onde-, et -and, y, e- donc -so, pues, quindi, portanto-, or -yet, sin embargo, tuttavia, contudo-, ni -neither/nor, né, nem- et donc car, le dernier, qui en anglais signifie ce qu'a écrit la reine Araceli, because, ou plutôt 'cause puisque c'est the sorter way, en espagnol et en portugais porque, en italien perché, en roumain pentru că (il y a cinq langues romanes, l'espagnol, le français, l'italien, le portugais et le roumain) et en espéranto...ĉar tout simplement ! https://www.google.fr/search?q=translate

Ok... maybe that's it.. '-' Thank you!!