This is one of the most common idiomatic expressions in French. It literally means “that walks” but we use it to say “ok, that works”. You will hear it very often in general conversation! Tu apportes le dessert? Ça marche! “Do you bring the dessert? Ok, that works!”. If you prefer to be a bit more formal, then you can say d’accord.
Be aware, if you hear it in a restaurant, it means “coming up”.
French with Valerie 