The programs I use to GFX design are mainly Photoshop CS6, and Cinema 4D for 3D texts and modelling.
There are other programs such as Gimp, in which you can use over Photoshop, but that comes down to preference (highly suggest Photoshop, though). Also, there's programs like Adobe Illustrator for vector art, Adobe After Effects for visual effects (animation).
It's really up to you to decide which type of graphics you'd like to make and the programs best suited for it. Good luck.