What kind of theory do you mean? History of design? Or theory of shape/mass?
What comes to my mind - Donald Norman's Design of Everyday things - its mostly about cognitive thinking, theres a lot of theory that you can apply to product design, although I think its more useful for interface design or similar...
Also his Emotional Design, that one should be more product-oriented... He also has "Design of Future Things" - havent read yet, but want to...
I had a look at Design Secrets: Products - this one is more "commercial" book, it has a lot of pictures, sketches, etc...
You should have a look at Universal Principles of Design, its a great reference of design phenomena full of interesting facts, really easy to read... if you google a bit, I think I have seen it somewhere as a pdf...
This is just a few that I know of, I would like to hear other ideas about cool books!
When I started (some 10 years ago) I began with Sketchup. It was great for understanding the basics of making forms with specific measurements and tolerances. After awhile though, I learned that I needed so many plug-ins to try and do what I needed on a more professional level that I quickly outgrew the software. I now use Spaceclaim, which is close in functionality in terms of how you manipulate objects, but so much more robust. There is a free version you can try called DesignSpark.
Fusion 360 is also highly recommended, as many of my friends use it instead, but it just wasn’t for me/wasn’t a fan. Either way though, I would maybe suggest getting your feet wet by finding forms/objects that you like the aesthetics of, and working through how you would re-create it as dictated by the material it is comprised of (wood, plastic, metal, etc).
slightly less "pretty" but ...
if you google linear slide there are lots of types.
Have you read The Design of Everyday Things?
Another interesting read would be The Evolution of Useful Things.
Have you read The Design of Everyday Things?
Another interesting read would be The Evolution of Useful Things.