@coolbean @snacks It's all mostly 2D sketches that turn 3D with some operation. Draw how something should approximately look from a perspective and it will be like that after some operation. Nobody sets constraints and dimensions correctly the first time, it's an iterative process all the way to the end.
A computer case is probably one of the harder things to design as someone starting out though. Mostly because of all the standards and dependencies on various dimensions. A RasPi case is a better thing to start with while keeping it computer related. And even that requires some measuring, tolerances and whatnot. I started with shafts, bolts and mounting brackets for example.