Chrome Extensions  are small software programs that can allow you do lots of different things from within the Chrome browser. When installed, the extensions appear to the right of the address bar.
You can get extensions from the Chrome web store, and there are plenty of useful free extensions. See end of page for information about managing extensions.

Extensions can be managed via the right click context menu for each extension:

Sometimes extensions cause unforeseen problems and need to be disabled or removed entirely. You can access all extensions from the chrome://settings/ menu and selecting Extensions.