I was on the same boat as you. The “Learn Fusion 360 in 30 Days” series on YouTube is awesome. In the first video you make a working Lego brick, and after a couple of hours I could make my own simple parts. Complex objects still seem hard, but simple household 3D prints turned out to be easier than expected. I started with OnShape but switched to Fusion just so I could follow this tutorial. I think (hope) the skills will be pretty transferable to any CAD.

https://www.youtube.com/watch?v=d3qGQ2utl2A