Note that those are two very different things in Orbiter.
A space station is a vessel, or an assembly of vessel "modules" docked or attached together (there's a subtle difference). With stock Orbiter comes module1 and module2, one being a cylinder and the other a node, they are not very pretty but are there for demonstration. The idea is to launch the modules atop of rockets, like with the Velcro Rockets addon, and use other vessels (DeltaGlider, ShuttleA) as tugs. A more elegant way is to launch them via the Shuttle and use the RMS arm.
A surface base is a location defined by longitude/latitude coordinates on a planet/moon. By editing the config file (see the doc) you can position objects around the origin (0,0,0) using a metric xyz coordinates system. Those objects are not vessels, only static, or sometimes animated (solar panels) 3D meshes or 2D sprites (runway lights). There are also launchpads, runways, and navigation beacons that are quite specific surface objects.
UGCO bases is a technique to build interactively surface bases in the sim. Basically, you land somewhere, drop boxes all around (the UGCO containers), add some water and "pop", they unpack into buildings. Technically, those are vessels.