GXP / BB30 are two different bottom bracket standards. You need to know which one your bike has and order the same type when you get your Red group.
GXP-type bearings are in cups that screw into your bottom bracket...BB30's bearings press in.
If you have a BB30 bike and want to use GXP, there are adapters available (not the other way around; BB30's spindle is wider)
This is the difference (GXP on the top, BB30 on the bottom)
Doubletap controls all the shifting with one lever, unlike your Shimano group (where the brake lever controls upshifts).
On a SRAM bike, you press the Doubletap lever until you hear a click.
if you release it after the first click, you'll go down a cog.
if you keep pushing until the second (or third, or fourth) click, you'll go up that many cogs.
That's all there is
