Click the Selection menu in ArcMap then click Set Selectable Layers. This will open a list of available layers that will allow you choose which layers you want to select when editing. For example, you might want to select a large number of buildings by drawing a box around them; but as you drew the selection box, you selected a parcel by mistake. To avoid this, you might uncheck the Parcels layer in the Selectable Layers list so that parcels cannot be selected.
See also: Editing features