Hi James,
You only need to adjust the needle valve. On the far side of the image which we can't see (but which you can see because it's in hand) there is a large nut which screws onto an industrial gas cylinder or a fire extinguisher having similar sized connection. If this were mounted to an industrial gas cylinder you would tighten the big nut on the cylinder spud and then fully open the cylinder's valve.
Check the sticky in the tutorial section for Fire Extinguisher (FE) type installation.
The colored gauge is the high pressure gauge and tells you the remaining pressure in the cylinder. The gauge on the right is the low pressure gauge and it tells you how much pressure is headed out towards your tank. This pressure varies as you manipulate the needle valve. The gas will bubble up through that glass vial (with the brass connections). Your CO2 hose connects at the top and towards your reactor. Make sure the vial is filled with water or glycerine and that the top and bottom brass fittings are very tight, otherwise the liquid in the vial will quickly escape.
Cheers,
