Have you ever opened a program that covers the entire screen? You can no longer see your Start Menu? There is a keyboard button that will bring up the Start Menu. It’s located at the bottom left of your keyboard, often called the Windows Logo button. Press it and you’ll have your Start Menu. Another way is CTRL+ESC.
While I usually use my mouse for most everything, there are a few occasions to use the keyboard shortcuts instead. This is especially helpful on a laptop when my external mouse is not connected. Here is a list from Microsoft on keyboard shortcuts.