What type of wall in my house?

Tap the wall with your fist to locate a hollow between studs. Next place your right elbow in your left hand and strike the wall firmly and flatly with your fist. You're not trying to break the wall - use just enough pressure to dislodge any filler between lathe strips. If you hear anything falling down in the wall it's a good bet the wall is plaster and lathing. If it just sounds hollow chances are it's sheetrock or drywall. A plaster wall may require plastic anchors and a screw to catch the wire of the picture frame, whereas a sheetrock wall may only require a small nail or nail/hook assembly. Shelves that may have to carry additional weight should be anchored to the wall studs. If their just for a few nick-nacks then you should be able to get away with butterfly anchors.