What are you confused about? Mounting it? Hooking up the wires?
I've installed two Autometer gauges and it's not that bad. The red wire goes to a power source - mine goes into an ignition wire in the steering column. The black is ground - a bolt somewhere behind the dash. And the 3rd wire for the A/F gauge - couldn't help you since I haven't wired one up. But IMO, the A/f gauge is kinda worthless. A true oil PSI gauge or temp gauge is a better investment.
-Melon