Open the GECK, load the Fallout3.esm and the Pulowski.esp + select the Pulowski.esp as active file. Go to the place in the capital wasteland that you'd like your shelter to be positioned at. Then place a door in the world. If you don't know how to place an object into the world or find a cell, start anew with the beginners tutorial. Really, this is like the first thing all tutorials will teach you. I won't bother explaining because there are enough tutorials on that topic. Then open the the shelter's cell via the cell window and double click the entrance door. Go to the Teleport-Tab and uncheck the teleport function, or you won't be able to assign this door as target for the door you placed in the wastes. Done? Then go back to the door you placed in the wasteland and double-click that one. Select the Teleport-Tab again and choose the cell of your favourite shelter. Then select the entrance door of that shelter. Save the mod, load it and play it. Won't look nice, because there's only a door in the middle of nowhere, but once that works you may want to start to work on a real bunker entrance by placing more objects around the door. Maybe a bunker entrance build into the side of a hill? But seriously: it's easy. Placing objects and linking doors is really one of the first things a new modder learns. So redo the tuts and work through them...