Advanced keyboard shortcuts are a new Roll20 feature for power users which provides a greatly extended set of keyboard shortcuts from the default. You can turn on advanced shortcuts under the My Settings tab, check the box next to "Use advanced keyboard shortcuts."

These advanced shortcuts are simple keystrokes, and for the most part do not use modifier keys such as Ctrl or Alt. Some of them are sequence shortcuts. For example the shortcut for the Shape Tool is "f r", which means pressing the "F" key followed immediately by the "R" key one after the other. Also note that these shortcuts are only active when you aren't typing in a textfield (such as the chat input box). You can press "Esc" at any time to de-select any active text boxes.

If these keys don't work for you, you might be using the Default Keyboard Shortcuts.