All the DCC decoders available today are dual mode i.e. they can run on both DCC or DC, so you can run a DCC decoder equipped loco on a DC layout, but you would need a DC power pack/ controller to do that. It's not a bad idea to have a DC controller you can hook up to a test track (but not with the DCC one at the same time), because all manufacturers suggest testing of DCC locos on DC first, the theory being that if a decoder will run on DC control OK, it should be fine once setup for DCC. Sounds a bit convoluted, but that test track can also be used as your programming track for DCC. One of the big differences and what gives DCC it's advantage over DC, is this ability to give locos their own individual identity (address) thereby enabling more than 1 engine to operate independently of another or others on the same track.
If your previous experience has been with DC operation, then there are new ways of thinking regarding how your trains operate. With DC, you control your engine via the amount of voltage you apply to the track between generally 0-12V. If you place another engine on the same track, it will do exactly the same, at the same time, 0 volts=stop, 12volts=flat out. With DCC, the track is at a constant voltage all the time (about 14V or so for most). All of the speed and anything else is done by digital signals (commands) sent from your Cab, via the track power, to the loco's decoder. That interprets the commands and converts it to activate the various functions.
Once you understand those differences, you'll appreciate your systems advantages.