The airline you're asking about is probably Ryanair (FR). Other discount airlines use STN as well, but Ryanair has the most flights.

It should take about two hours by car - around the M25 clockwise, then out the M11. Not difficult directions to follow, but the M25 can be very congested at some times of day. Other options include the Heathrow Express into London, underground or taxi to Liverpool Station (no change on the Hammersmith and City tube, but be warned that its "Paddington" stop is a long hike from where the HEX lets you out, not in the same place as the other Paddington lines) and the Stansted Express out. If your trip will be during a weekday rush hour the trains, even though London will be crowded, are less subject to absurd delays than the M25.

(I'm not a moderator, but since this doesn't seem to have much to do with miles/points I wouldn't be surprised to see it moved to the London forum.)