CO2 bottle to reg & demand valve to beer engine - HELP!

[BritishBelgianTwst]

The time has come, I've got all the parts now I just need a helping hand to tell me how to put it all together (and use it, well not the drinking part - I can work that out myself!).

So I've got the following:

CO2 bottle from Norm
Single regulator from Norm
Corny from Norm
3/8 beer lines
Maxi 110 from Norm
Demand valve from Norm
Beer engine from Norm

Plus various JG fittings from Harmony Hut.

The bits I'm wondering about how to connect are:

CO2 bottle to reg to corny
and
demand valve to beer engine

I think that I just need to:
1. Screw my reg onto the CO2 bottle and then run a 3/8 beer/CO2 line to my corny. Could someone also let me know how they both work! Do I just turn open the valve on the bottle and then control the flow with the reg therefore leaving it open to maintain a specific pressure when serving?

2. Connect the demand valve to the Maxi 110 with a 3/8 beer line and then connect the flexible hose from the demand valve to the bottom of the beer engine. One question I have is what are the two JG fittings on the beer engine for?

Thanks for your help - I'll drink to all your health once I've got a new brew in the corny.

[Trunky]