Odoo 9 reorganised the parts of the system an administrator touches most. Here is the tour we gave clients at the time, in the order you meet the screens.
Note: this article was written for Odoo 9.0. Menu names have changed in later versions, but the concept and the configuration logic still apply. Ask if you want the current-version equivalent.
Database management
Starting the server shows the list of available databases. From the login screen, Manage databases (or /web/database/manager) lets you create, restore, back up, duplicate and delete databases and set the master password, all from the browser.
The settings dashboard
Settings now opens on a dashboard: number of installed apps, active users, how far each app has been configured, and a direct Invite users box. General settings (email servers, import and export) stay under Settings; every app's own options moved into that app's Configuration menu.
Apps dashboard
All installed and installable apps are reached from one Apps screen, with search and an upgrade indicator per app.
Developer mode
Technical menus (models, fields, views, actions) are hidden until you activate developer mode from the Settings dashboard, which keeps day-to-day users away from them.
Together with the redesigned list and form views, these changes made 9.0 the first version where a non-technical administrator could run a small company's instance without help for most tasks.