C'est ça - Ça va - D'accord - Voilà

C'est ça : We say "c'est ça" when we want to confirm what the other person has just said.

Ça va: We say "ça va" in a variety of situations. Here are 3 examples.

a) in answer to the question "Comment allez-vous ?" or "Comment ça va ?"

b) when we are trying some clothes, for example. If they fit, "ça va"; if they don't, "ça ne va pas, c'est trop large".

c) when we agree to what the other person has just said.

D'accord : We say "d'accord" when we agree to a proposal.

Voilà : We say "voilà" when we give something to somebody "voilà votre clé" or when pointing to someone or something "Ah, voilà Marc !" or "Voilà la tour Eiffel à gauche".