One of the easiest and most common 3D modelling programs is Sketchup. It’s free, very versatile, and has a lot of tutorials and demos that you can access. This is a good place to further your understanding of 3D Modelling.
Sketchup is now web-based, so it can be used right in your browser. You can access the free version of the application here.
Here are some tutorials that you should work through to learn more about what Sketchup can do.