Question

what is a alt key and how does it work

Answer 1

a key on a keyboard that when pressed at the same time as another key gives the second key an alternative function.

Answer 2

The Alt key (pronounced /ˈɔːlt/ or /ˈʌlt/) on a computer keyboard is used to change (alternate) the function of other pressed keys. Thus, the Alt key is a modifier key, used in a similar fashion to the Shift key.