To reply directly to your questions:
A "CV" is a "configuration variable". In decoders, they have a number of things that can be configured. That configuration is done via numbered CVs. For example, the "primary address" is configured via CV 1.
There are many ways to program CVs.
- One way is to program using a throttle via the command station, such as your Digitrax system. You didn't mention which Digitrax system or the throttles you have, but the manual that came with your Digitrax system should tell you how to do that.
- Another way is to use hardware/software combination to program CVs. For example, using a LocoNet to USB converter (like Digitrax's PR4) and JMRI's Decoder Pro. If Decoder Pro knows about the particular decoder you are trying to program, it can take those CV values and make them more "user friendly". For example, Decoder Pro might give you a bunch of checkboxes to choose some options from instead of you trying to do binary arithmetic and converting from binary to hexadecimal and/or decimal.