[newbie formula help]

hi all im just starting to learn basic electronics from a book and i am in need of some help on resistors in series and parallel . im stuck on the formula for parallel resistors eg:-

1 1 1 1
---- = ---- + ---- + ----
Rov R1 R2 R3


I think it is some form of algerba but i dont know any of that .can someone explain it in simple terms or a website that will .does it mean divide or multiply. i know that Rov means overall resistence and R1 is the value of a resistor ,but how to work it all out i dont know

thanks mado21 ???