You can get the free "Personal Use" version of Fusion360 here:
https://www.autodesk.com/products/fusion-360/personal
I've been using it on and off for quite some time now. It's partially cloud based, meaning an online connection is required for some processes, it has some handicaps made in when it comes to file conversions, shouldn't be an issue for a casual user. Upside is it automatically updates on the fly, Autodesk releases new capabilities and adds them to 360 for the general public to test.
Most of the open source type free cad packages like FreeCad will work on similar principles, from the look of their website it looks pretty capable. As long as the software will output STL files it should be a decent starting point.