I've made a large number of custom prints, and all of them were created using TinkerCad. It's an amazing toolkit, stupid easy to use but versatile. That is ... until something needs a tiny adjustment somewhere. That's when I feel it would've been neat to use parametric CAD instead.
I have spent many hours following Youtube tutorials for Onshape, Fusion, and FreeCAD. Tutorial shapes like a LEGO brick are fairly easy, although I admit that this kind of modeling is a sharp departure from the kid-friendly TinkerCad.
My problem is that I don't want to make simple coasters or keychains, but complex shapes like this one. It's a holder/mount for two different kinds of walkie-talkies that I use, and the blue part slides into a tray in my car's dash where it sits nice and snug.
Question: How the hell do I even get started modeling something like this?? There's not a single straight cuboid here. Everything is slightly wedge-shaped.
The way I do this in TinkerCad is that I build the hollow first: I made a 3d model of the walkie, a little oversized, set it be hollow, and drop it into the shape - that's the red or orange shells you see.
That is because the holders go around an injection molded part and you need to add draft to injection molded parts to ensure they can eject out of the mold. Every CAD software worth using will have the feature. You just model the part with straight sides and then add the drafts in a later step (before you add rounds/fillets). The features generally work by picking some references to define where the draft starts from, which direction to pull the surface, and the surfaces or edges you want to draft.
Honestly, the parts you show are super basic. If you sat down for an hour and read documentation on the basics in Fusion360 you would be able to replicate parts of that complexity no problem.