Using Route or Tracback with GPS172c

[seaeagle]

Hi , I have a garmin gps 172c plotter & i am after some tips on using it for plotting a channel into a creek. To use the trackback, the manual says to save the track log. Do you have to mark point A & when you get to the end mark point B & save?? Or is the better option to use the Route & mark each turn etc
Thanks