Stone blocks
Stone is produced from rock rubble via a Stonecutter's table after it is researched. To create stone right click the table, click 'Bills', and use the + and - buttons to set how many pieces of rubble you wish to consume. You must have a colonist with 'crafting' enabled in the Overview menu. Stone blocks are always produced in batches of 20 per rock chunk. Stone can also be obtained by deconstructing abandoned structures that are randomly scattered throughout the map, though these must be Claimed first.
Cut stone can be used to supplement other valuable resources, namely steel and wood. It can be used to craft walls (even the conduit walls that carry electricity), or fancy floors with faster than default walk speed and less mood penalty. Cut stone can be used to craft everything from doors, automatic doors, tables, benches, to beds and royal beds. It is also the prime resource for crafting sculptures for colonists with the Artist skill.
While doors made of stone are very hard for enemies to destroy, they also take a long time to open, so consider making the Autodoor variant to save time. It also doesn't give nearly as much rest effectiveness as wooden beds do.
Stone walls and structures appear to take 3 times as much damage from explosive weapons (like Mortars) as structures made of other materials.