Hi. Welcome to the board.
As far as how to assemble the regulator - you shouldn't. Take it to your local dive shop and ask them to do it. If you bought the regulator elsewhere, you should expect to pay for this service, but it's worth the money.
If you make a mistake, even in something as simple as screwing the hoses together, you can end up paying an even higher price. Never mind the potential for a leak, you can easily damage the soft brass and even softer plastic, thus ruining the regulator. Of course, if you make a bad enough mistake and the thing comes apart underwater, you can get hurt or killed.
Mostly it isn't complicated but staying within the limits of your training extends to working on your gear, too. Get the training and you won't need to ask here for instructions.