Pipes, or pipe sections, are used as components in the construction of screw pumps. You can't build pipes by themselves in the current version, nor connect them to form a conduit - to move water or magma from one place to another, see aqueduct.
Pipe sections can be manufactured from wood at a carpenter's workshop, from metal at a metalsmith's forge, or from glass at a glass furnace. A glass pipe section is called a tube. They are stockpiled as furniture.