Odoo 9 just released with huge changes in views and settings. Let see the overview.
We start with database management.
When you start your Odoo 9 server you will be prompted with list of databases available. Like the image below.
Then you can select your version 9.0 database and click on it. You will be prompted for user name and password to login.
You can manage your database by clicking on Manage databases or using this url http://localhost:8069/web/database/manager . You can Create, Restore or set master password directly from here itself. You can also backup,Duplicate or delete a database directly from here.
If you want to change the database you can click on  as shown in the image below.
When you click on Settings you will see the dashboard. Which shows you all information together. Like how many apps are installed on your database. How many active users you have in your database. How much you have configured the installed apps and last but not least the social share to spread the word.
You can directly invite new users from here itself.
Then you have General Settings where you can define the settings like email servers, import / export etc..all individual apps settings are moved under their respective menus. Check image
All your apps can be accessed from the Apps menu. See image below
To activate the debug mode just on the right side on top menu click on the icon (?) as shown in image below and click on About and Activate the developer mode.
you can then have different options in the debug view(a bug icon) drop down on each model view
You can also directly compose a new mail from clicking on mail icon on top right
in the menu bar.
you can also check notifications received by clicking on notification icon next to mail icon on top menu right side.
You can change your preferences from the drop down menu that occurs when clicking on your login name on top menu right side.