I'll give you a basic idea of what it does, if you want more info on installation I will be glad to help. A SAFC is a very basic, but effective tuning device. It only modifies the maf signal that the ecu sees, therefore you can tune how much fuel your ecu adds. It adds or subtracts fuel on an RPM basis.The wires you tap into are:
Power/Ground
RPM signal
Throttle signal
MAF signal
I have my neo set up to display RPM (the exact number), Throttle percentage, and Battery voltage. There are a few cool ways to display the data like digital and analog gauges. You can also have any color combination you want.
If you want to tune yourself you will have to get a wideband to show your A/F ratio (I highly suggest the AEM UEGO, very accurate, pretty cheap). All you do, is have your friend hold a video camera so it can see the RPM gauge (factory or SAFC) and the wideband gauge at the same time. You do a pull through one gear (third or fourth). Look at what the A/F is at each 500 RPM increment, and take fuel away at that RPM till your wideband shows the number you want all the way through the powerband.