When I hook up to a trailer I have to connect 3 lines.

Red (emergency air) green (electrical) and blue (service air)

The green just plugs in, and the air lines just use glad hands. Super simple.

The green line is fairly self explanatory it runs power to the trailer for the lights etc. The air lines however, are a bit more interesting, to me anyway.

The blue line is controlled by my break pedal and works similar to a car's hydraulic breaks. Press the pedal and the truck stops.

Where trucks with air brakes really differ is the emergency line. Truck breaks, by default, are locked. If you spring a leak in your break lines in your car, you can't stop. If I spring a leak in my lines I can't go. My emergency line supplies air to the breaks to prevent them from locking up.

There's an air compressor under the hood that runs air to several things beyond the brakes, including my suspension and the seats in my cab. My break lines always leaking to some extent, it's not like the glad hands are the most secure connection on the planet, but as long as there is adequate air pressure in the system, it a works just fine.

I have no idea if this is interesting to anyone, if it is ill post more in the future, if not, I won't.