In reality, wormholes are purely a scientific conjecture, a consequence of the same equations that describe black holes. They have not been detected in real life, unlike black holes. It's been theorised
that tiny wormholes may constantly appear and disappear in quantum foam. However, capturing these, stabilizing them and expanding them to useful sizes are all impossible with current technology (and for all we know, may never be possible). Actually stabilizing a wormhole would theoretically require "exotic matter"... which would have, among other never-encountered qualities, negative mass... Needless to say, wormholes have remained a curiosity in the field of physics, and are certainly not being considered for practical travel anytime soon.
Fiction, of course, is different. Wormholes are often used as a potential way to get past that bothersome "can't accelerate past the speed of light" rule, using the wormholes as nodes in an interstellar Portal Network. In fiction, wormholes take on all sorts of forms, including confusing them with black holes, which are a naturally-occurring scientific phenomena in which all energy and matter are attracted to it (also known as having a lot of gravity); nothing can escape the event horizon of a black hole (though if FTL were possible, the event horizon — being based on lightspeed as an absolute limit to escape velocity — would need to be redefined), let alone the singularity at the centre (as things would need to, were they to act as most theories of wormholes state). Sometimes they can be opened at will, sometimes you can transmit radio waves through them for communication, sometimes they connect you to parallel universes, sometimes they are used for Time Travel, and so on.
The theory around wormholes gives them various properties not generally shown in fiction. To begin with, a wormhole would consist of two (probably spherical) mouths connected by a throat. Another property is that sending something through a wormhole would affect the wormhole as well, a phenomenon known as back-reaction. For example, if a mass were to be sent from one mouth of a wormhole to the other, the entry mouth would gain mass and the exit mouth would lose mass. This kind of Equivalent Exchange means that wormhole travel would require moving equal masses in both directions, to keep the mouth masses balanced. Another property is that wormhole mouths could be moved around. A civilisation capable of using wormholes at all wouldn't need spaceships, it could shoot one mouth of a wormhole to some distant planet and keep the other mouth at home, and then it would be possible to basically walk from one planet to another.
