Creating milage expenses allows you to easily track and submit your milage costs. Input your start and end addresses and the app will calculate the milage for you. If you have to take additional stops, or divert from the direct path, you can update the actual miles driven from the value which is created when the destinations are input.
If you need to mark it as a round trip, just input the same start and end address. Toggle "Round Trip" to on, and the milage will double. If your actual route differs, you can manually adjust the total once you've turned on the Round Trip toggle.