How to you fill up the system?

Hi there, I've had a pressure valve replaced due to it leaking. The heating guy was ok draining the system, but doesn't know how to fill it back up again! any help appreciated otherwise its going to be a cold night!

Graham

Still no joy getting someone out that knows what they are doing, these things must be rocket science lol.

I keep hearing a clonking noise now and again, boiler switched off at mains so I guess it's a pressure valve of some description. Appears it should fill on it's own but it's just not. Is there anything I should get checked?