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Oh, Inkscape would be an excellent program for that! However, even though it might not have as many features as a CAD program, there still will be a learning curve. Inkscape does call itself a professional vector graphics tool, and we finally see the long awaited version 1.0 on the horizon!
There's a graphics program called GIMP, which is primarily a raster graphics program, but it does have some simple vector tools. If you want simplicity, you might prefer that. (Although note that the tools don't work exactly like Inkscape's tools.)
However, assuming your invention would need a drawing similar to what you showed, I would still recommend Inkscape first. That's because, as you start to learn, and you gain more and more skills, I think you'll end up being happy that Inkscape has more advanced features than you thought you needed at first.
If the drawing of your invention would be less detailed or less complex than what you showed, you could probably get by with GIMP.
If you go with Inkscape, I would start with Help menu > Tutorials > Basic, Shapes, and Advanced. Don't worry, the one titled advanced really isn't advanced. It's actually the introduction to the tools you would need to make such a drawing. It's probably the one you need most.
After that, move to other tutorials, such as you can find on the Home tab, above. There, I have tutorials organized generally by skill level. So you can start with the Beginners block, and pick out the tutorials that you need. And move on to the Intermediate block when you're ready. Also, in Help menu > Inkscape Manual, find the Quick Start chapter. That's a short series of tutorials as well. One of them in particular would be good for you (drawing the logo for a hiking club, I don't remember the exact title).
And finally, I guess this is my opinion, but you'll probably want to try out some programs before you make a decision. I always advocate for new Inkscape users to jump in with both feet!