I just need to know the index numbers of certain edges and faces in a cube in blender. Is there anywhere a diagram of that? Or can this be shown in blender as e.g. the length of an edge.
Blender doesn't normally display the indices information but it does have a debugging feature that can display them. To enable debugging you type
bpy.app.debug = True into blender's python console. Once enabled you will find an indices option in the mesh display panel of the properties region (press N to show the region) while in edit mode. Only the indices of selected items will be shown and your selection mode will define whether vertex, edge or face info will be displayed.