Now that everything is working, switch off again, turn your Beeb over and connect a disc drive.
The ribbon cable goes in the right-most socket. Most disc drive connectors will only fit in one way but just for certainty, the red strip on the cable should be to the left. If you put it in the wrong way, the drive light will illuminate permanently when you switch on again and nothing else will happen.
The power lead will only fit into the power supply outlet one way. It is an unusual plug so make sure you align it properly before ramming it home.
The BBC Model B can cope quite happily supplying power to a single drive but it won't entertain a double drive so don't even try. Make sure you have a mains powered double drive if you are going to use it with a Model B.
If this picture doesn't look right to you then you have probably never actually turned the Beeb over when fitting a drive. Everything is of course the other way round when you are rooting about underneath your Beeb to attach a drive because you can't be bothered to clear all the discs, EPROMs, joysticks, second processors, leads, tapes, screws and cups of tea off the lid to do it properly!