This command really should be called "take the layer effect like drop shadow and put it on a new, separate layer". Of course that would make the palette menu much too wide, so Adobe went with the abreviated name. This is what is does: it takes the layer style - in this case a drop shadow...
and creates a new layer with the layer style on it.
The original layer style "disappears" and the effect is no longer "tied" to the layer, so make sure the effect looks the way you want before you use this command. But, it's a great way to turn a drop shadow into a cast shadow (with Free Transform) for example.
(You'll find the command under Layer>Layer Style>Create Layer)