Blender is probably the best place to begin learning 3D modelling. It's completely free and there are 100s of resources available on youtube/online that will teach you the fundamentals. There are also heaps of plugins available for blender that can make certain types of modelling a lot easier, especially when you're starting out. It does take some time to learn but it's a lot of fun and once you get a handle on it, you can make some pretty awesome stuff.