Welcome to the Guild!
We specialize in maps of fiction, which certainly includes RPGs like D&D, Traveler, HARP, RuneQuest, D20, etc. But others are creating maps for board games like alternate versions of RISK. Some create maps strictly for miniature war gaming. And some are illustrations for fantasy novels.
CC3 can be certainly used for RPG maps, but works equally well for any other kind of game map - board games, war games, what have you. CC3 isn't exclusively for any one kind of game.
Only thing is CC3 is ideal for overland maps, you might require DD3 for Dungeon designs, and CD Pro for City Designs, though CC3 can stumble through those other two. ProFantasy has a suite of applications - so that's one thing to consider.
Another direction would be to go the route of Inkscape/GIMP, which are basically FREE versions of Illustrator/Photoshop. Note these applications are fairly complex with steep learning curves, but we have a boatload of tutorials to get you in the direction you need to go. These aren't mapping apps per se, rather graphics apps - both vector and raster art.
Visit our software list to learn about all these applications...
You might also start with our introduction to digital cartography, here...
It really depends on your goals, your skills, what you're willing to learn, and whether you want to spend money on it.
I for example use Xara Xtreme Pro 3.2 - a hybrid raster/vector graphics application for all my mapping, and I'm almost alone here to using this software - only because I use it in my day job and am very familiar.
There are so many directions to go, I don't want to choose for you!
Again, welcome and start exploring - once you got software, start checking out our avaialalbe tutorials (which may help you decide on software as well.)