Recipes are items dropped from Creatures. When used, they unlock a crafting recipe which is randomly assigned to the item recipe. It is a good idea to start with slimes and nightmares. If you go into the complex detail of it, each biome has a certain set of recipes. Basically, in the snowy area there are wooden things, the snowless area lets you get stone things, the Cave of Ringing Wind gives some iron things, the Oil Valleys give other iron things and tantalum things, and finally Sunglade gives grass and soronite things. Each biome will give more things than that but that is the gist of it. For example, the oil valleys can give wafers which is not iron or tantalum.

FTS Recipe

A player with a recently dropped recipe beside them.