Subdivision Surface Problem

Is there a way that I can add a Subdivision Surface to only one part of an object?

I want to smooth the corners of my gun, but I don’t know how to do that without smoothing out the entire thing…

Thanks!

Very common question and the answer is yes and no.
Subdivision surface modifier and multiresolution modifier affects all the faces in your object so no, but it’s possible to do localized subdivisions.
If you select faces and W -> subdivide, you’ve subdivided a part of your object (and most likely created ngons). Also beveling an edge (ctrl+B) or beveling a vertex (ctrl+shift+b, blender 2.66a) creates localized subdivisions *, as does dynamic topology in sculpting (blender 2.66a).

  • not subdivision as in face subdivision, but added geometry

This is where subdivision surface modeling basics comes in and where you need to know how to control it with the topology. When you have a reasonable amount of subdivision levels (2) in your added subdivision surface modifier, you want part of the object to be sharp edged while other parts should remain smooth.
Moving another edge loop closer to another edge loop makes the faces between the loops smaller than faces around them, this contains the subdivisions to a smaller area and you get a sharp turn in the face flow. When you want sharp edges smoother, you move edge loops further away from each other to make them smoother in relation to other faces around them.