From their website, "Tinkercad is a free, easy-to-use web app that equips the next generation of designers and engineers with the foundational skills for innovation: 3D design, electronics, and coding!"
There is an excellent workshop from the University of Victoria Libraries here: https://uviclibraries.github.io/3d-design-print/.
Blender is an open-source tool that you can download and install on your Windows, Mac, or Linux computers. It is a little bit more advanced than TinkerCAD.
Here is a good beginner tutorial on using Blender:
For more advanced tutorials, see the list on this creativebloq.com page.