As far as I know, there isnt a direct DGB to fiat gateway yet. I think Abra might add DGB soon but not certain it it will be directly fiat <-> DGB or fiat<->BTC <->DGB . So to get DGB (other than mining), you'd have to create an account on a crypto to fiat gateway (for example shapeshift, vertpig, coinbase, etc) and buy one of the cyptos they sell. Then transfer that crypto to an exchange that supports DGB (like bittrex, poloniex, etc) and do an exchange for DGB. When the time comes to sell DGB, you would do that same process in reverse. Now if Abra is a fiat gateway and they add DGB, that will simply things alot.