hi I am doing the mold tutorial in the online tutorials of solidworks 2007
the tuturial is of a telephone.

in the telephone part's tree you can see that whoever built it did a surface offset of zero and a surface extend.

I am rebuilding this part for learning purposes

I have two questions?

1.why are these two steps done?
2. how come when I do the surface extend I see material yet when it's done in the tutorial there is no material or it seems transparent...