JMRI is a great FREE tool for interfacing your DCC system and your layout.  It is used for everything from programming decoders to complete layout control.

You can get your free copy here. 

Without getting to complicated the best way to get started is to install the program and have a look around.  You will notice that 2 options come up.  Decoder Pro & Panel Pro.  If you are only wanting to program decoders then Decoder Pro is all you will need.  If you are looking for layout control then Panel Pro is what you want.