Press Windows-E to open an Explorer window. Click Documents on the left-hand side to open your "My Documents" folder. In this folder, find and open the folder named The Lord of the Rings Online.
In The Lord of the Rings Online, you need to have a folder named Plugins. If you don't have that folder, create it now by clicking New Folder at the top of your Explorer window.
Open the Songbook zip file you downloaded from lotrointerface.com, and drag the folder named Chiran out into your Plugins folder.
If you run LOTRO now, you should be able to type /plugins load songbook in the chat window to load the Songbook plugin. NOTE: If you were already in LOTRO, type /plugins refresh before loading Songbook, or LOTRO won't see the new plugin.
Any questions, feel free to speak to me in-game. :)