Look at the image below. The top row buttons have been labeled F1 - F10 to make it easier to explain. Google Support explains what each of these keys do:
Some special keys sit along the top of Chromebook keyboards. If you're using a Windows keyboard with your Chromebook, the F keys at the top of the keyboard will work just like the keys below.
Go to the previous page in your browser history (F1)
Go to the next page in your browser history (F2)
Reload your current page (F3)
Enter Immersive mode, which hides the tabs and launcher (F4)
Enter Overview mode, which shows all windows (F5)
Decrease screen brightness (F6)
Increase screen brightness (F7)
Mute (F8)
Decrease the volume (F9)
Increase the volume (F10)
Search your apps and the web at the same time. On a Chromebook, this key is located on the side, where you'd normally find the Caps Lock key. If you're using a regular keyboard, the Windows key in between Ctrl and Alt will work as the search key.
Tip: To turn Caps lock on temporarily, press Alt + the search key.
Citations
Images are from the Google Help Center.