For information on 1.12 recipes, please refer to GyroStudioTechnology's page on the mods. Many recipes are for 1.10.2, thus outdated.
This page is currently in process of being created (8/25/2020)
Railcraft ores do not follow normal ore generation, and instead generate in very large mines. Retrogeneration may be required to find these veins, but new chunks are your best bet using this mod in an already existing world. Mines consist of an area where a large amount of one Railcraft ore will be present along with your regular generating ore. It is not a structure and rather something you will find while mining normally. You can use the config to turn this form of ore generation off if you wish for it to generate like vanilla ore.