Bedrock is a natural block (that you can also place) found in the Fossil layer just below the surface or in shallow Caves, together with Stone, Limestone, Fossils and Magnetite.
You'll need to equip a Stone Mining Cell or an even better Power Cell to pull / mine Bedrock.
Obtaining Bedrock is one of the requirements to unlock the crafting recipes each for the Forge and for Bedrock Walls.
Bedrock is then an ingredient to craft the aforementioned Forges, but also Bedrock Doors, and a number of building blocks like the Bedrock Wall.
Bedrock can also be used to craft Stone Slabs and/or Stone Rods in a Processor (no crafting recipes are needed for that).
Bedrock Slabs, Bedrock Slopes and Bedrock Columns can be produced in a Processor from Bedrock Walls that have to be crafted first.