I have a Boulter Camry Quartet boiler with no pressure!?

Hi guys
Non expert female here, my radiators are hot at the bottom but cold at the top. Bleeding the radiators neither gives me air rushing out or water. So I checked my pressure on my boiler and it's zero ! How do I get the pressure increased please - I have large round cover with square Riello cover below. Is there a hose/valve I have to open - if so where is it, and which way do I turn the valve? Sorry to sound dence but I'd hate to get it wrong and break it :-(
Thanks v much