Turn right out of the site down Dean Lane and you'll find the A23 at Hooley. Turn left for Merstham, or right for Coulsdon South. Parking is easier at Merstham. Timetables are available from here http://www.southernrailway.com/timetables.php
Generally there are 2 trains each way per hour to/from London Bridge Mon-Sat, journey time about 30 minutes. You can change at East Croydon for fast trains to Victoria - trains every 3-10 minutes depending on the time of day. On Sundays Merstham still has 2 trains per hour, but they alternate between London Bridge and Victoria.