Unless you require unusually complex designs to be created, I think you'll find the easiest 3D modeling software to be Tinkercad. It is browser based, which means any computer with a browser, regardless of the operating system.

The program allows the user to manipulate primitives (geometric solid shapes) by adjusting the size and placement. The program allows the user to convert a shape to a "hole" to subtract portions of other shapes. There are alignment tools that permit precise positioning.

Exporting is a simple button labeled Export, to STL, OBJ and I think 3MF formats, as well as SVG for laser cutting.

There is a substantial amount of tutorial information on the internet, especially YouTube. The program is mostly intuitive.

If, over time, you find that the program isn't powerful enough, there are other options, but Tinkercad is a good starting point.

I'm a big fan of OpenSCAD, but it's a text editing type of program. One creates similar primitives, but rather than using drag-and-drop, it's done in a scripting manner. Not for everyone, but certainly programmer people who want to explore 3D model creations have a head start.

Once you have a creation that you want printed, consider to drop me a message. I'm not a 3D printing service, but I can do quite a bit at the hobby level at far lower prices!