I have created a shapefile in ArcCatalog by right-clicking the folder I want it in, then selecting new, then shapefile, then changing the type to "polygon", and using the British National Grids under the projected co-ordinate system.
I then tried to add the shapefile in ArcMap by clicking the Add Data button and selecting the shapefile I created.
My problem is that when I open the shapefile in ArcMap, the map is still blank and I cannot see the projected shape of the British National Grids.