They can be as simple as a frag tank attached to your display and sump.  Most pests cannot make it from tank to tank, so this is pretty good but probably not 100% for the super-anal folks.  This is what I do now - observe and dip between the tanks.  It is not worth my time to do anything else.
Having a completely different system is the ultimate.  Some people change their display water into the QT tank, but I would never do that - you can get backwards contamination.
I keep the same lights and parameters as in my reef.  If you keep the frags/corals in there for long, you will need a way to replenish the major and minor elements.  I keep a small fish and some shrimp in there to have some nutrients - damsel, cherub angel, few emerald crabs and four peppermints are my current residents.  They get flake every few days.  I do keep some rock and sand in there for more stability.
My process: I currently only get stuff from people that I trust.  However, I don't trust anybody...  I remove stuff from the plugs and get new plugs ready.  I dip in Coral Rx and observe.  If I see something funny, then bayer, but rarely.  Coral QT for a while until I am seeing good growth, no pests (AEFW bites for me)... this can be anywhere from two weeks to a few months.  Then, when I am ready, I remove them from the plugs again, CoralRx dip and put them in the display.  In the case that I take something from the display to the coral tank, then I dip there too.