From the homescreen of the app, tap the End session for… button.
When prompted, tap Really log out.
The app will upload your work to the server, release your current work list, and log you out.
You should always end session at the end of your shift. The means that every day when you download your work, you have the latest, up-to-date version of the programme. If you do not end session and just carry on with the same download the next day, you will not see what others have done and may end up duplicating work.