Hello sms58,
If you see a screen like this:
your MacBook Air has a firmware password set. Even if there is a firmware password, you should be able to start normally into macOS, but can't boot into other disks or the recoveryOS.
Try starting your Mac without pressing any keys. If you still see this screen, your keys might be stuck.
To disable the firmware password, see here: Set a firmware password on your Mac
If you forgot your firmware password, you will need to schedule an appointment with Apple. You will need your receipt or invoice as proof of purchase.
If it's something else, let me know and I will try to help.
See also: If your Mac doesn't start up all the way
Hope that helps!