By default the Chromebook uses a two finger tap on the touch pad instead of a right click to bring up context menus (or any other action that a right click would produce).
Sometimes the taskbar or "Shelf" will obscure the very bottom of a web page. If you right click (two finger tap the touchpad) the Shelf or long press it on the touch screen you should see an option to reposition it or auto-hide it. If you select auto-hide - the shelf will only become visible if you hover the mouse pointer at the bottom of the screen or if you swipe up from the bottom using the touch screen.