For anyone who is a savvy MS Excel users, PS Actions translate to using Macros in Excel.
They are preprogrammed / (or recorded) steps. It's useful if you like applying the same technique over and over without having to go through all the steps one-by-one.
Just click the PLAY button and off it goes, all by itself.
Love it.
Below is a photo set I used utilizing different actions in PS.
(the top photo is the original)