Well that is a really poor choice for gaming computer, but I assume this is a 760 Dell Optilex right and you're on budget? They don't usually come with a Video Card, so basically you could get any Mini ATX video card from AMD or any Mini ATX from NVIDIA series like 700, 900 or 1000 like a GTX 1060 Mini or GTX 1050 Mini, although I think you'll experience some bottleneck while running games because of it's processor, but thats the best you can do for a rig like this and maybe trying to upgrade your RAM a little to 8 GB instead of 4 if possible...
As for Counter Strike GO you are good to go I guess, since these are the minimum requirements..
cpu: Intel Core 2 Duo E6600 or AMD Phenom X3 8750 processor or better
CPU Speed: Info
ram: 2 GB...