While Gimp can help you edit raster images (pixel graphics), Inkscape will help you edit vector graphics. The good thing about vector-based images is that you can resize it as you wish and it will not be distorted.
If you’re not a professional graphics designer most likely you’ll be able to use Inkscape and have it do everything that you need. No need to purchase the expensive Adobe Illustrator or CorelDraw.
Inskcape will handle several file formats such as: SVG, PDF, EPS, AI, and also JPG, PNG, GIF. It’ll work on Linux, Windows, and MacOS X operating systems. Download it here.