Jumpgates are huge structures left behind by the Annunaki or Ur alien civilization. The jumpgates are long ring-like structures that have a diameter of several kilometers across, they are opened by a device called jump engine, and the route is controlled by another device called the jumpkey. Humanity has very little understanding of the principles at work behind the gates.
Jumpgates are hoop shaped and vary in size between 200km to 1000km across. They are entered slowly, for safety reasons and always from the sun facing side. The image within is always of the target system at the time of the last jump. After a jump is made the gate needs time to reset itself.