And now we are talking about affiliated, you could also search Google....
,
right tamlin
Anyways, layerstyles.....
it depends on what you do with photoshop, if you manipulate photographs I don't think you will need them much. But If you make logo's, websites or other art from scratch...they can be very helpfull.
You can make layerstyles yourself by right-clicking on a layer and select layer style.....there you can tweak al kind of settings to make the layer more realistic, or not depends on your choice. You can add things like inner-/ outer- glow, shadow....
Layerstyles can also be downloaded, in that case someone else has tweaked and changed teh settings until he got something he/ she liked. If you download such a thing and add it to a layer, you can tweak the settings in the menu from above....
Hope this helps a bit, and I think you should check out that site of tamlins they are most of the time very helpfull!!