I got started doing layouts and PCB’s for guitar pedals (I have quite a few projects available over at the Madbean forum).
My first board was for an EHX LPB… about as simple as it gets for guitar pedals!
I use Eagle for board layouts, and inkscape for any graphics layout/panel drawings. I’ve always ordered boards from OSH park.
For eurorack I’ve complete layouts (and PCB panels) for passive mult’s, attenuators and a couple of simple LFO circuits.
Mutable Instruments and Music Thing Modular are very good resources to see how others approach eurorack PCB layouts.
The Madbean forum is also great resource for Eagle tutorials (it’s a very friendly place too). e.g.: http://www.madbeanpedals.com/forum/index.php?topic=9661.0