More serious designs are basically the same as what's said here, it's just spread over more pages. You often have special labels that designate that it's connecting to something on a different page, or hierarchical/multi-channel blocks which can be confusing because there isn't really a standard way of showing that, so it's often vendor specific. You get used to the main ones after a while though (Mentor Graphics Pads/Xpedition, Cadence Allegro, and Altium).
This YouTube series is quite good if you want to see a very complicated design - it takes you through the schematic/layout of a dual-Xeon server motherboard: https://www.youtube.com/watch?v=FXZJ6jrpIKU
A good source of schematics for learning is often development boards - for example, the BeagleBoard ones - https://beagleboard.org/hardware/design
This YouTube series is quite good if you want to see a very complicated design - it takes you through the schematic/layout of a dual-Xeon server motherboard: https://www.youtube.com/watch?v=FXZJ6jrpIKU