You can start right away using Tutanota. If any question remains, check our detailed how-to: https://tutanota.de/howto
This describes all Settings of Tutanota. It also answers common usability questions like:
How to send an encrypted email?
How to switch to not confidential?
How are contacts sorted?
How to add / rename / delete a folder?
How to upgrade to Premium?
How to set up an alias?
How to send an email from an alias?
How to manage passwords for my Premium users?