Rip current

[Nautically Challenged]

I was at the beach in Ft Lauderdale yesterday and the current was extremely strong. Although the waves were following the north east direction of the winds, the current in the water was going south: very strong! In a minute the water could take you in a hundred feet away (along the beach of course, providing you don't go deep).
Anybody knows what cause rip currents and has anybody ever being taken by a rip currnet? What is the best action to take when taken away?