Pressing "R," by default, will show your recipe book.
Crafting recipes are available for learning from public or player vendors. You can only learn from a purchased recipe if your skill is high enough.
Many recipes can be "discovered" simply by trying to put the right items into the crafting window from your inventory. The number and type of items matter and just adding all items does not work. The "craft" button is highlighted green if the combination is correct for the combination of items for a recipe. When the item is crafted, the recipe is saved in your recipe book. For example butchering recipes are easily discovered if you drag one carcass or fish into the craft window of a butchering station. You can not discover recipes for which you don't have high enough skill yet.
You can teach other players recipes too if they are labelled "re-teachable". To do so open a trade window with another player and your recipe book and drag the recipe icon into the trade window.