Once you have a route on the unit, zoom in and touch and hold part of the trail. release and then select follow route.
Finally you can follow the arrow which points the way.
When you first switch the unit on, it will automatically start tracking you, at the end of your walk/run etc, select cross hammers, overlay and save as. select kbd at bottom right of screen and save
I'd hate to sound pedantic but this information is in the User Guide. It is on page 6 under the heading 'Viewing your GPS Position' and on page 7 under the heading 'Working with Routes, Marks, and Tracks'