Install AutoHotkey using the link called "Installer for AutoHotkey_L" at http://www.autohotkey.com/download/ .
Run AutoHotkey from your Start Menu to create a sample file called "AutoHotkey.ahk" in your "Documents" folder. Open "AutoHotkey.ahk" from your "Documents" folder in a text editor.
You can comment out all the sample commands by putting a "
;" at the beginning of each line. Add the following text to the end of the file:
These commands assign:
Win+, → Volume Down
Win+. → Volume Up
Win+/ → Volume Mute
If you want to use other keys, briefly read "Basic Usage and Syntax" in the help file -- particularly the subsection "Key List".
Create a shortcut in the "Startup" folder of your Start Menu pointing to your "AutoHotkey.ahk" file in your "Documents" folder, and run it. The script will run each time you log in.
If you change the contents of your script and want to recompile it: Log out and log back in; or right-click on the "AutoHotkey.ahk" icon in your system tray and click the Exit command, and then run the shortcut in your Startup folder again.