Tutorials are great for this sort of thing, often the solution is easier than you think. And in most cases if you want to do something, you're not the only one, so it's probably in the program somewhere.
Bear in mind a "part" usually defined as a single solid part, soon as you split it in some way you have two solid parts and you are on your way to an "assembly".
Learn to use the "stack" or "browser" or whatever they call the list of things you have done. You can often move things up and down the list and solve things that "break" when you change something else.
Constraints and Dimensions are a blessing and a curse. As a matter of course I usually delete all constraints of any sketch I create, cause I KNOW I'm going to have to change something. And when you add a dimension ... you are not measuring something, you are carving in stone what that dimension is, which will constrain anything attached to it, you can edit the dimension to change it, but you can't drag the object to change it (most of the time). So only use dimensioning on things you absolutely want to stay the same dimension no matter what (unless you edit it).
I figured out a long time ago that software this advanced is for people that know what they are doing when it comes to manufacture and design ... I am NOT one of those people
What is outstanding about 3d printing is you can design the part and then just send it over to the printer and have it made (well, that is somewhat over simplified). What hooks you on CAD is designing something you need that solves a problem ... opens up a whole new world.