You should get into the habit of logging out when you have finished your session - here's how
To log out when on the main start screen (standard version), click the logout button, top left
To log out when on the main start screen (simple version), click the logout button, bottom left
Most of the screens in Flow360 also have a logout button near the bottom of the lefthand side bar. Simply click to immediately end your session and logout.
When you log a new Helpdesk issue you have the option of saving the issue and logging out all in one go by using the Confirm & Logout button, top right.