This component allows you to read the important messages that you receive after installing (third-party extensions) or after updating (third-party extensions and Joomla! itself). To access this component, select Components (1) → Post-installation Messages (2).
Once you've opened the component, you will see a panel displaying the admin messages (1) as well as information about the latest release of Joomla! (2):
Component Post-installation Messages with notifications
On this screenshot, you can see that Joomla! announces the addition of a new feature to the CMS since the version 3.2.0: the Two Factor Authentication feature.
The feature's details are introduced here and you can even enable it by following the instructions.
Once you've read the messages, you can hide them by clicking on 3. You will then see the following page:
When you access the admin control panel, you also get a message telling you that you have unread messages:
Component Post-installation Messages on administration control panel