The universe is a large space, light years across, containing several 'Star Systems' (Systems).
There are some details about individual systems in the 'Guide to the Galaxy' menu.
Each system is a relativily small (a few km across) box. The ship's location inside it is displayed by the 'position' indicator.
However, like asteroids, the boundaries 'wrap' (only this time it's a 3D cube rather than the 2D screen.)
If evrything is working you, and everything else, should able fly and shoot through 'wrap' without knowing it's there (apart from the position indicator going negative).
Each system has differing characteristics. These effects the value of things when trading
Travel between systems is achived by passage through 'Hyperspace'.
Hyperspace is connected to each system via a 'Wormhole'.
To get to another system:
For now hypespace is navigated using the same engine and mechanics as other systems. Eventually some form of 'Warp Drive' will be required.