In court just dress smartly, be polite to the magistrates, plead guilty and look ashamed of yourself. (If you've not got a solicitor, it might be worth asking to speak to the duty solicitor when you arrive at court. He/she might be able to offer further advice).
You've not stated what you've been charged with. Fairly obviously, it will include 'driving otherwise than in accordance with a licence'. That carries 3 to 6 points on your licence. Fines are determined, in part, by your income but I'd guess at around �300 (plus, perhaps, about �30 costs)
If the police and CPS have bothered to charge you for driving without lights, that could add a further 3 points but probably wouldn't involve a further fine.
When you pass your test, and get your full licence, you'll have to drive extra carefully for the first two years. If you commit a motoring offence, during that period, which brings your points total to 6 or more, your licence will automatically be revoked. For most new drivers, that would mean that they'd lose their licence after two speeding offences. In your case (because you'll already have points on your licence), a single speeding offence would be sufficient to see your licence revoked.
Penalty points remain valid, for totting up purposes, for 3 years but they can't be removed from your licence for 4 years. (There are certain offences for which points remain on a licence for longer but they're not relevant here).
When you get your own car, your insurance will increase because of your conviction. For an experienced motorist, 3 (or even 6) points might add very little to their premium. However, you might find that you'll be paying considerably more. (For example, most 17-year-old new drivers are quoted around �2000 per year for a car in a low insurance group. Your quotes might be in the range �2500 to �3000).
Chris