Click your avatar/profile picture in the top panel on the right and select PARAMETERS. The settings are divided into the sections GENERAL, NOTIFICATIONS, and APPS.

In the General section, you can change the language, document presentation style, attachment display mode, and the default document opening mode.
The Notifications section is used to configure notifications coming from the application (e.g. regarding requests awaiting approval).
In the Apps tab, you can configure the order of applications displayed in the side panel, as well as the order and visibility of specific columns in the views of individual applications.