You may already know this but the Nurburgring actually consists of 2 parts (the Nordschlief and also the new racing circuit - sometimes called the sudschlief). The two parts are connected however most of the time the nordschlief is barriered off from the sudschlief. The Nordschlief is the part that is generally open to the public however some days the track is hired for different clubs.
The accepted norm is that you overtake on the left hand side so if you stick to the right hand side of the track faster drivers/ riders will easily be able to get past. The track is around 14 miles long and there is a ticket barrier at the start. You can get single lap tickets, multi lap tickets, week and season passes. The price per lap reduces depending on the number of laps on your pass. Typically though its around 22-15 euros per lap.
If its your first time then don't worry and just ride at your own pace. The track is open from spring to mid autumn and there's more people there on hot days and weekends. Road cars can lap at the same pace as many large capacity sportsbikes if driven by somebody who knows the course so bare this in mind. If you have an accident then your vehicle will be removed from the track and you will have to pay the recovery fee plus any damage to the armco etc. The track is shut down for accidents and uses a normal flag system to inform people already on the track if there's an obstruction ahead. If there's an accident then you would normally be expected to finish your lap and exit the course whilst course staff organise any recovery/ medics.
If the course is shut due to an accident then I would recommend waiting about 10-20 minutes after its opened to let the loopy bunch back on the track and get rid of their frustration at not being able to do as many laps as they would like.
There's nothing to be worried about so I would just suggest you take your time until you know where the course goes and just enjoy yourself.