Ilya Radchenko- Web App Developer, AppGeoIt's free. Start there and you'll be able to pick up other software. The most important things to learn are modeling, texturing, composition, and lighting.
thomas ross- Startup analyser and investorFor modeling, I would say Blender is far and away the best free option. Blender also includes powerful sculpting, animation, UV mapping, physics, programming, post production and rendering tools. Nearly everything Modo, Maya or 3DS Max can do, Blender can do just as well.