The stuff I used to use was easy... just draw on the traces you want with a sharpie, then dunk it in etching solution. You can print transfer them too, but you have to be careful to touch up afterwards, otherwise there may be breaks in the copper.
It just keeps the etch from soaking into the copper pretty much. Yeah, it's easy
The hard part is doing it without breaks (though most are easy enough to fix with a bit of solder). Unless you have a printed layout, it's damn near impossible to get the layout perfect too.