So, FreeCAD. It's a beautiful hot mess. There's a 1.0 in beta right now that's bringing some much needed changes.

FreeCAD has a lot of parallel capabilities; it has an architectural workbench for drawing buildings, a Drafting workbench for more traditional 2D drawing, the Part workbench for a weird kind of boolean approach, and the Part Design workbench for a more typical sketch-and-extrude parametric modeling workflow like Fusion360, Inventor or OnShape.

The workflow is you create a sketch and draw a 2D shape, and then extrude (FreeCAD uses the word Pad) it into 3D space, then you can draw further features on that to design the shape you want.

The basis of how it works is somewhat unintuitive at first. "Parametric" means you draw using rules. There's a piece of software out there called OpenSCAD that is a very pure implementation of this because you "draw" by typing code in a kind of programming language. FreeCAD lets you represent rules by drawing things with the mouse. Rules like "this is a straight line. It is parallel to the X axis. It is 5cm long. The leftmost endpoint is 3cm from the X axis and 4cm from the Y axis." There's only one way to draw that line. Those rules may be called Constraints or Dimensions. The powerful part is you can later change one of the rules, like "Did I say 3cm from the X axis? I meant 4cm" and it'll redraw the whole part for you. Get your head around that concept and CAD software will unlock.

The UIs are different, but the general concepts are similar for FreeCAD, OnShape and Fusion360, sometimes tutorials for one will be useful for learning the others.

Yeah abandon FreeCAD for now. It's a powerful FOSS option, and the new v1.0 looks promising, but I second TinkerCAD to learn. It's intuitive, and most of the principles you learn will translate fairly easily to other CAD software. Unless you're trying to sculpt organic shapes, I'd focus off TinkerCAD

I second tinkercad for super basic parts. Need to print a knob for a radio that isn't on thing-verse? 20min in tinkercad.

For blender basic things to learn could be plugging a hole in a part and adding a smaller or bigger one to match the screws you have on hand.

Or cutting a part in half to extend it, fill in the gap.

it made no sense to me

That's all CAD software. You can't just jump in and intuitively learn it by just doing it. It's like trying to learn a programming language. You need a solid tutorial to explain the basics, at a minimum. Even with something simple like TinkerCAD.

FreeCAD was probably the worst choice. Give TinkerCAD a try. I know the FOSS community will hate me for saying this, but I like Autodesk Fusion for a full featured CAD package. It has a very steep learning curve, like all CAD software, and you need to watch some videos first. You will make a ton of mistakes and do even simple things wrong at first, but once you get going, it's great to use.

Tinkercad is in the browser, super easy to use.

I'm both used CAD software professionally to do engineering and developed CAD software professionally, and TBH I, too, find FreeCAD difficult to use.

(I haven't tried the latest versions that are supposed to be better yet, though.)

Tinkercad is just combining basic shapes, so there's basically no learning curve.