Problem with extruding a face, please help!
 

Hi, I'm trying to model a box with thick sides and figured that the only way to do this is by extruding the faces (please correct me if I'm wrong). However, when I extrude the face it doesn't make it thicker but rather moves it as you can see in the picture:
http://i.imgur.com/35Zf5n7.png?1


How can I fix this? Or is there a different way to thicken faces?

To make it thicker use scale and by that i mean those three colored squares.

For example select all faces and scale them inwards. You'll see what i'm talking about.