Explanation

Modifier keys = They modifies the action of another key when used together for example to shutdown/restart our computer: ALT+F4 alphanumeric keys = Alphabates + Numeric alpha means alphabates that include the letters A to Z/a to z. and Numeric means numbers 0 through 9. function keys = F-keys they are F1 through F12. They have assigned special function by the operating system. Function keys are also used with Modifier keys for example to shutdown/restart our computer: ALT+F4