open up a weapon and start loving around
I personally used the Mini-nuke as a base for my first gun; I swapped the model and colors, changed emitters, explosions, damage values, etc to get used to the language
it'd probably be best to use something else unless you're okay with your first weapon being ridiculously overpowered, cuz chances are you're gonna beef it up before you nerf it
after that I learned sketch-up, used the Pro version trial to export my things, and used DarkStar's blender tutorial to get them in game
keep in mind this was with absolutely no prior experience with torque OR blender, both are very user-friendly and easy to get used to imo