It basically specifies how much you've been active as a member on GAG. If you gather enough, you can redeem it for certain things, and being above level 8 for example makes you not get advertisements anymore.
"GirlsAskGuys utilizes a point system to recognize every member of the site for the invaluable expertise they provide to our community. The point system is based on the actions a member takes, such as asking questions or sharing opinions. This point system also encourages a greater level of participation with more value given to better opinions. "
First up XP and Xper are same thing - You may be mixed up in points total and levels - The points total is just a picture of how active you were and the levels are when you hit certain totals. Welcome to the site - I hope you enjoy yourself here - Anyway don't worry after a few days all will become clear to you and if you don't understand just ask like you just did here.