There are two ways to approach the “software learning curve” for newbies: You can begin with a “hobbyist/Beginner tool” which will be good enough for most small home gadgets.
But, something more grown-up (professional grade) is UltiMake’s Cura product. Here’s a video to get you started:
One of the more sophisticated ways to lay out a Printyed Cricuit Board (PCB) is to lay it out using a program like Eagle to route the traces and export to a file structure which can then be turned into G-Code. Here’s how this series begins.
Once you get a board built, it’s just a matter of getting components and installing and soldering.
Long ways to assembly, sometimes!