If you are asking how to install:-
Download and unzip, put the script to the following folder:-
PC: C:\Program Files\Adobe\Adobe Photoshop CS#\Presets\Scripts
MAC: <hard drive>/Applications/Adobe Photoshop CS#/Presets/Scripts
where # = the CS version
If Photoshop was open close and restart it so that it can pick up the new script.
To assign an action and function key, start recording a new action, assign the function key you require, then from the action palette fly-out menu select "Insert Menu Item" now File - Scripts and select your new script. Stop the recording.
Now every time you press the function key it will run the script.