If you press the? key while on Twitter and not composing a tweet, reply, or sending a message, an overlay will appear that displays all of the available keyboard shortcuts. The old user interface also has a Keyboard shortcuts overlay that can be opened by pressing the ? key. The keyboard shortcuts are the same as the new user interface, but there are some differences between the old and new user interfaces. The shortcuts that have two keys and a plus in between them, means that you press those keys in sequential order, not at the same time.
Source: https://www.bleepingcomputer.com/news/technology/how-to-use-twitter-with-keyboard-shortcuts/