I guess from what you have said you have driven only a 4stroke kart, in an arrive and drive chassis, at somewhere like lakeside???
The next step is to drive a proper kart, well one that actually is quick!!
For this i would try Club 100 (
www.club100.co.uk) on one of there test days, where you do not need a kart license, or own any race kit,like suit and helmet, just turn up and drive!!!!
If you find you like driving these 2strokes then the next thing is either race in club100, where you do not have to own anything to do with the kart, or buy your own kart.
If you go the own kart route you need to look at
www.karting.co.uk and look at where your local tracks are. Then get yourself down to the track and start talking to people, with regards to running a kart, how much to buy, etc, etc, etc
Hope that helps abit, but ask more questions if not....