Now, you know that Chrome OS is full of handy keyboard shortcuts for things like reloading a page or going to your home page in the browser. In fact, there are so many that it's almost impossible to keep track of them all. Finding out just what you can do so you know which ones to remember is easy. Press Ctrl + Alt + ?, and you'll see an overlay of the keyboard with all the key functions and shortcuts. Soon you'll be a pro and Shift + Alt + L-ing and Alt + Shift + B-ing all over the place.
Note: The above comes directly from their article. Click here to read more.