Welcome aboard! [#welcome]
I’d imagine we’re similar in age. My HO trains went up to the attic in the late 1960s, and I resurrected them early in this century. I’ve upgraded most of my rolling stock to metal wheels and Kadee knuckle couplers, and I’ve bought a lot of new equipment, too.
DCC is Digital Command Control. Your old HO trains ran by putting DC voltage on the tracks. The higher the voltage, the faster the trains ran, and the polarity of that voltage determined the direction of travel.
Fast forward to the present day. Each locomotive has a microcomputer on board, and the DCC base station sends signals to the individual engines to give them commands. As we sometimes say, with DC you run the track, but with DCC you run the trains.
Only a few DCC systems operate from a fixed base station. They either use wired hand-held throttles or a radio link to give us completely wireless throttles.
Those on-board microcomputers, called decoders, are getting more elaborate all the time. Many have on-board sound systems with both automatic sounds, like motors or chuffing, and manual sounds like bells and whistles controlled from your throttle. There are also stationary decoders, which can be used to throw your turnouts from your throttle.
Thanks to the NMRA, DCC is highly standardized, so any DCC-equipped engine will run with any DCC base system. So, you are not locked into a particular manufacturer, and can pick and choose to find the engines and decoders that you like.
I’ve been using DCC for years now, and I think it’s one of the best thing that’s ever happened to the hobby.