Resources are sources of a variety of different yield in Civ 6.

Resources are sources of a variety of different yields (Food, Production, etc.), and some provide other special bonuses to a civilization. They appear in certain hexes. Some are visible at the start of the game, while others require the acquisition of specific technologies before you can see them. To utilize a resource, it must be within your civilization's borders and you must construct the appropriate "improvement" in that hex. There are three types of resources: Bonus, Luxury, and Strategic.

Bonus resources can increase the Food, Gold, or Production output of a hex. Bonus resources cannot be traded to other civilizations. These resources can be "harvested" by Builders to remove the resource and provide an immediate, one-time sum of Food or Production to the city that owns the hex.

Luxury resources increase your civilization's happiness by providing Amenities and provide a small bonus to the hex's yield output. Only one source of a specific Luxury resource provides Amenities.

Strategic resources are not always visible at the start of the game—they may require knowledge of a particular technology before they appear on a map. Strategic resources allow you to build certain units. When you construct an improvement on a Strategic resource hex, it allows you to build units that require that resource (i.e. Musketmen require Niter) in any of your cities that has an appropriate district—Encampment for land units, Harbor for naval units, or Aerodrome for air units. If you build an improvement on 2 copies of that resource, you can build or purchase those units in any city, whether it has the appropriate district or not.

For a list of all resources, see: Civilization 6 Resources