Train shows are a good place to wade into the DCC issues. Usually the shows will have operating layouts where you can watch the trains run on DCC and you can ask the members questions on how DCC works.
The lights, sound and operating control of the locomotive is all by digital command. Each locomotive has a small decoder which isolates the loco from the track. All voltage and computer signals go to the decoder first and from there, power is directed to the features of the locomotive by your control of it with the hand held controller. Just like operating a printer that is linked to your computer. It does nothing until you issue a command with your key board or mouse. You can print a document. You can clean the ink heads. You can change color of ink on the paper, etc. The decoder receives its digital commands through the rails along with the operating power to run things. The controller is usually hand held and is either plugged into the layout or it has radio link to the layout. Either way, the hand held controller will have present function buttons to basic control of the loco. Horn, lights, bell, speed, direction, etc. For sound, the loco will need to have a speaker installed along with a sound producing decoder. The same for various lights on the loco. You need to have the light bulbs or LEDs installed in the loco and properly connected to the decoder to work. You can buy the components and install them yourself or you can buy locos with everything installed, ready to go. Whatever the features are in the loco, your handheld controller can control it without modification. When you finally get the hang of all this, you can download programming software (free stuff) and setup a programming track to customize the sound features of your locomotives along with the lighting features.
Take it one step at a time and you can build upon what you already know.