Access keys are keyboard shortcuts that allow you to operate apps using a keyboard instead of a pointer device such as touch or mouse. You can access the desired function by pressing a combination of Alt key and one or more alphanumeric keys in order.
Controls that support access keys have key hints that appear when you press the Alt key. For example, when you press the Alt key on the barcode reader screen, a key hint of “C” appears above the camera button. You can access the camera function by pressing the C key in this state.
Access keys that use one alphanumeric character support keyboard shortcuts. For example, you can use the keyboard shortcut of pressing the Alt key and the C key at the same time to access the camera function on the barcode reader screen.
(Reference) Keyboard shortcuts for apps that come with Windows