Blender is a fine tool for me. You can use Sketchup (is a free program to download) to practice the concept of 3D modeling. Once you feel confident enough, you can pass to Blender and follow the tutorials there. Learn the key bindings first (not all of them, just the fundamental ones) and the various tools that will help you (such as the mirror to make 2 sides of the object in one go).
Then you should pass to orthogonal drawings and how to position them correctly. If you have already got experience with technical drawings at school, it's a plus for you. Finally, try to extrude your way to success