To completely understand the concepts, I recommend reading several different things. Start with the Wikipedia page on Wormholes.
I also recommend reading two of the Stephan Baxter novels Manifold: Space and Manifold: Time.
There are different types of theoretical wormholes. One of them is bidirectional (Lorentzian), another is unidirectional (Schwarzschild). For the rest of this, I'm assuming we're talking about a Lorentzian wormhole.
Making a wormhole
As you mentioned, wormholes are not stable if you send photons or matter through them. However, if you can first thread them with a material called "negative matter" (not antimatter), then you can maintain a stable wormhole and send information and matter through it.
Negative Matter exhibits negative energy density and negative gravitational attraction.
Thread the wormhole with negative matter (in the shape of a cylinder perhaps) and then matter can flow through the center of this cylinder (sphere, geodesic dome?) without collapsing the wormhole. The region of space inside the wormhole is not any sort of hyperspace or "+ dimensional space". It is normal space that represents an alternative path between two points.
This path distance will always remain identical through the wormhole but the end points may be move through non-wormhole space (essentially allowing us to move our wormhole destination points).
By putting one of the wormhole end points on a ship that travels at relativistic speeds and flying it around, we could set up the wormhole to permit moving through time too (read the manifold novels for a better treatment of this subject).
I imagine that in appearance the wormhole would have some similarities to the one portrayed in Stargate franchise but the opening would always be on, would be bidirectional, and you'd be able to see through it at all times. For someone passing through the wormhole, it'd be like stepping through normal space without any observable change when passing through the opening.
The wormhole will always link its end points as a short distance through the wormhole, even when those points have wide separations in time or space outside of the wormhole.
I suspect that because the wormhole requires a rare and exotic type of matter, that if we found any of it we would not waste it trying to make space in the wormhole throat for a convenience store. There really wouldn't be any need to do so anyway, just put the store adjacent to the wormhole opening on one side or the other.
Although a wormhole's endpoints will always be linked (this opening always connects to its linked opening), you could move them about in regular space.
So you could, for example, create your wormhole bridge, move one end into Europa's ocean and the other onto the surface of Mars, open the doors and flood the surface of Mars. Or put one opening in the fuel tanks of your interstellar ship and the other in a deep part of Earth's oceans. Voila! Instant propellant tankage without having to carry the propellant around with you.
To everything involved, the region of space inside the wormhole would appear as normal space in every respect as long as the negative matter kept the wormhole throat open.
Mapping the wormhole connection points through the wormhole wouldn't be hard. Two linked points always remain linked. OTOH, since you can move the end points in normal space your maps would have to account for transport of the end points.
You could even pass a wormhole through another wormhole with no ill effects.
So your maps would need to be updated with the movement of those wormhole endpoints.
Just bear in mind, we have never observed negative matter. If it does exist, it likely only exists in extremely minute quantities in our region of space. So although this exotic material would be extremely valuable to us, it would be an extremely limited resource. Use your negative matter and wormholes wisely you might not be able to make many (any?).