Refined resources in Astroneers are those that are created by smelting natural resources which you can harvest from the terrain of each planet.
Metals are the most common refined resources as these ores, in their natural form, have little to no use in crafting items and structures.
Refining natural resources is a simple process. It will require the player to have constructed a smelting furnace. This structure has 4 ports on the front that will accept various natural resources. These will be burned in the furnace and the refined resource will be output.
Smelting furnaces will draw from the bases power supply, making it difficult to build more than 1 of these in the early stages of the game. Building a solid power grid for your base is essential for creating a resource refinery in this game.
A full list of all of the available resources in Astroneer can be found in this wiki along with instructions on how to smelt them and what the resources can be used to create.