Formal:
* Vous êtes d'accord? (Are you in agreement?) - This is the most common and neutral way to ask if someone agrees.
* Êtes-vous d'accord? (Do you agree?) - This is a more formal version of the previous one.
* Je suis d'accord avec vous. (I agree with you.) - This is a polite way to express agreement.
Informal:
* T'es d'accord? (Do you agree?) - This is a casual way to ask if someone agrees.
* Je suis d'accord. (I agree.) - This is a simple and informal way to express agreement.
* C'est ça. (That's it.) - This is a short and informal way to say "I agree".
* D'accord. (Okay/Agreed.) - This is a very common and informal way to express agreement.
* Oui. (Yes.) - This is the simplest and most basic way to say "yes" and therefore express agreement.
The best way to say "you agree" in French will depend on the situation and your relationship with the person you are speaking to.