Logging out of the app is not necessary since the app is additionally protected by a PIN or your fingerprint.
If you do choose to log out, you will have to type in your email and password again when you will want to use the app. If you do not log out when exiting the app, you will need to type either your PIN code or use your fingerprint, depending on which method you have chosen, to access the app again.
To log out, start by clicking on More from your Dashboard menu:
Then click on Settings:
On the bottom of the page click Log Out: