So, just had a look a this track which I tried to do on Saturday and got a little lost navigating.

http://www.gpsies.com/map.do;jsessionid=F1D7703ED2D5C694DEA640B64375E34F?fileId=xrorajzyazoenjyp

What do I need to navigate by this? I use my iphone to track, but I want to actually use it for a ‘go this direction’ type thing. Do I need a gps unit? If so, which one?

Well, there are a number of apps that give you maps installed on the phone, like UK Map, Viewranger, and others that allow the downloading of map sections. Viewranger is the best, allowing you to record tracks, downloading other people’s tracks, it has compass and direction arrows to show direction of travel and direction of destination, you have a choice of 1:50k and 1:25k maps that you can download as map sections and tiles to suit wherever you happen to be walking or cycling.
I love Viewranger, but I use UK Map as well, because it allows the downloading of 1:10k tiles for free. Outside is a good app for OS maps as well, but neither allow trail recording.

A satmap will load up kml files or gpx files.

If you have the map orientated as ‘trail up’ then the map is rotated as to your direction of cycling and if you zoom in to a resolution of about 1:3k then it is quite possible to follow the route at a decent speed, as long as the accuracy of the recording is decent.