You can open the crafting menu with the C key. You'll see a list of craftable items, some of which may be greyed out - that means you have insufficient materials or tools to craft them. Items can be crafted with materials either gathered from the world or dropped by enemies. Food items can be crafted into even more effective foods, and some basic weapons and armor can also be crafted. You can search for a specific recipe at the search bar in the top left corner of the crafting menu. You can also search for recipes that use a specific item by typing input: and then the name of the item into the search bar.