It uses the GPS, you enter your speed and optimum time to start. Then you stand in the start box and start the app, and walk the course like normal. You stop at each fence and hit a button to mark that there's a fence or combination, and you can take a photo and make notes about each fence if you like. It automatically inserts the minute markers based on the time and speed you entered, and if you use a eventing watch that beeps every minute, it's increbibly helpful! Using this app and the minute markers, I have always made time! I love it! It beeps to mark the minute marker when you are walking the course, so you can make a note of where you should be. Of course you could always wheel your course and figure out the minute markers that way, but I like just using the app, I don't have to do the math and I don't need to bring anything extra with me!
After you're done walking your course is sets it all up on a map with markers for the jumps and minute markers, and you can "play" the course and it will walk you through. Here's a few of my courses from last year, just so you can see, you have the option to upload your course to the website afterwards, which is what I did. www.mycoursewalk.com/course_walk/show/510-South
Peace Horse Trials Alhambra Summer Event - Preliminary CourseWalk near Red Deer County, Alberta, Canada - Description
If you hit the playback button it will play the course and show the jumps for you. Green boxes are for each jump, and the white bubbles are the minute markers.