If you want to learn more things about Photoshop layer mask here is a layer mask tutorial that will teach you the basic things. You will find out how to add a quick layer mask, how to disable layer mask, and how to use filters to create more advanced layer masks:

http://www.psd-dude.com/tutorials/photoshop.aspx?t=layer-mas k-in-photoshop

hope you find it useful,
John