The bottom of the Chromebook desktop is called the Shelf.
It holds the:
Launcher - Where you find apps
Pinned/Open Apps - Apps that have been pinned or are currently open
Control Center - More information below.
Search Bar - which allows you to search:
Your Google Drive
Your Chromebook Apps
Apps - displays the most recently used Chromebook Apps
Up Arrow - click to expand the window to see all of the Apps as well as the Chrome Web Store
Select the app you would like to open.
If you don't see the app you are looking for, please note the dots along the side. You might have multiple pages of apps. Click to switch between the pages.
Or, if you still don't see the app, put the app name in the Search area and try to find it that way.
Do you use a particular app a lot? Well, you might want to pin it to the shelf so that it is easy to access.
Find the app you want to pin to the shelf
Right click on the app or tap and hold on the app
Select Pin to Shelf
Click on the User's Selected Picture to open the user's Control Center.
Here you can:
Sign out
Shut down the Chromebook
Lock your Chromebook screen
Open Settings
See your WiFi connection
Cast your device (See the Chromecast page)
Choose a keyboard - should be set to "US"
Set volume
Set brightness
See battery status