Oh your new. OK then.
First you need to find out what Android version you are on; 4.1.2, 4.2.2, 4.3 etc.
You can find that out in the settings. Once you find that out, go to Goo manager or goo.im and download the appropriate GApps file for your correct firmware. Now put that somewhere on your phone where you keep any ROMs or kernels and stuff off that nature so it's easy to find.
Go into recovery mode, select install/flash zip file, and find the GApps file you downloaded. Flash that and you'll be good.