The crafting category contains pages about how to craft, where to craft, tech trees, and crafting recipes.
Crafting, in the simplest terms, is a method of turning inventory items into other inventory items. Which items can be turned into other items is limited by which crafting recipes you have Researched and unlocked in your world. Crafting recipes are tied to specific Crafting Stations (blocks that craft items) or to the Character directly.
See Inventory and Crafting for more information about how to craft.