Solar systems contain one, two or three stars. The primary star is at the center of the solar system. In a binary or trinary system, the secondary star orbits the primary star. In a trinary system, the tertiary star may orbit the primary or it may orbit the secondary.
Stars usually have planetary bodies orbiting them. Solar output (based on the spectral classification and magnitude of each star) determines the radius at which the habitable orbit zone may occur. In this orbit zone, worlds may be habitable. Not all solar systems contain habitable worlds. Some solar systems have no planetary bodies at all.
See also: Planetary System
It is possible for a spacecraft to travel through space directly to another solar system at lightspeed using normal propulsion, this is known as deadheading and travel time can be quite long depending on the distance. A spacecraft with a FTL drive can however travel the same distance in a fraction of the time.
The primary star may have one or more naturally occurring wormholes present around it. Wormholes connect to nearby solar systems in a loose branching network. Spacecraft use wormhole drives to travel instantly from one solar system to another through wormholes.