Summary
Orbital assemblers are orbital platforms that use a combination of drones and nanobots to build large objects such as ships they can also be used to build space stations though they must be orbiting the same planet that the space station will be orbiting.
functionality
Orbital assemblers are different than orbital forges they do not manufacture parts instead they take the parts produced the by orbital forges and put them together this does not mean that an orbital forge is incapable of fabricating a fully functional object however some things are large then the build volume of an orbital forge or are simply not practical to fabricate using a singular forge.