cubemaps in blender?

I’ve just started using blender, and I’m a little confused as to how to apply cubemaps on an object. Also, how do I separate one part of a model from the whole?

I tried searching but couldn’t find anything…

Also, how do I separate one part of a model from the whole?

enter edit mode, select the vertices you want to seperate, then press ‘P’.

Cubemaps…do you mean environments maps…

In case:
http://www.google.dk/search?hl=da&q=blender+environment+map&meta=

when I press ‘P’, theres an error saying “cannot separate with vertex keys”. What do I do from there?