Supercruise
Supercruise is a method of "fast travel" within plantetary systems.
Activating Supercruise
Select a target within the current system via the Target Panel
Use ENABLE SUPERCRUISE control to engage super cruise.
Once Frameshift Drive is charged, throttle up to engage super cruise.
Use flight controls and throttle to manoeuvre at super cruise.
Maximum super cruise speed is determined by proximity to stellar bodies.
Use ENABLE SUPERCRUISE control to disengage super cruise.
Supercruise cannot be engaged if your ship is mass locked (i.e. too close to a large body of mass such as stations or planets), has its landing gear down, or has cargo scoop or hardpoints deployed,
NB: It's possible to Supercruise to other stars, but it'll take you several days (or weeks), so use Hyperspace for that. You are able to assign a button or key command to enable/disable supercruise. This is done via the client control options. The default setting is the "J" key.
Much of this is currently taken from Fangrim's Guide to Supercruising the Easy Way [1] on the official ED forums. Supercruise is currently in an early development iteration so is subject to significant change.
Other info on supercruise
In Beta 1.04, it's not possible to supercruise from one star system to another.
All star systems will remain at the same distance regardless of how far you supercruise in any star system.
For example, you can supercruise from Asellus Primus A to the Asellus Primus B which is 0.17 lightyear way, as both stars are in the same system.
However, if you try to supercruise from 26 Draconis to LFT 1361 (which is 0.33 light year away) you will find you're always 0.33 light away from LFT 1361. You can never get there in supercruise. This applies to all star systems.
Not that most people would even bother with trying to supercruise to another star system.
Max supercruise speed is 2001c. This speed take 57 min to reach.
It would take 4h 22m 51 second to travel 1 light year at max supercruise.
Just to travel the 8.208Ly to IBootis from Asellus Primus would take 1d 11h 57m 27 seconds.
Navigational Aids
The blue rings seen around planets and moons as you approach them during supercruise are just scaled up indicators of the planets radius. So the first one you see might be 1000 x bigger than the radius of the planet so when you approach it you can get a sense of getting closer as it grows in size (it's not actually moving or growing, it's just you getting closer). Once you get close enough it fades away and you see a ring that like 500 x bigger than the planet and so on. They're just there to show how you are approaching the planet when it's too small to see.