The turtles used a 20/10 breakoutsystem for entries/ exits.
ie if the price goes higher/ lower than the previous 20 periods high/low, a long/ short entry was made. The position was closed on a 10 period breakout in the opposite direction, defined in the same way.
There are a number of other rules about adding to poitions etc and strict money management based on volatility measures and position sizing.
Donchian channels as I understand it, would just illustrate on a chart, the previous high/ low of n periods so that you can easily see when the breakout occurs. (Not that it's difficult to see anyway).
Donchian channels are not something I use but I think the turtle system still works reasonably well on commodities/ forex etc on an EOD trading methodology. It's more of a long term, trend following method of trading though which not many people on here seem to subscribe to.