I have Mac desk top and I turned off the bluetooth and I turned off the wireless keyboard. When the Mac was turned off and then back on, it wants the password and I cant use the keyboard because the bluetooth is off. How do I sign in?

If you have a new Magic keyboard and mouse? Plug them into your Mac using their charging cables.

If not, dig out, barrow, buy a USB keyboard and mouse to sign-in, then access and turn the Bluetooth back on.

FWIW most any inexpensive USB Generic or PC keyboard and mouse, will work with your Mac and handy to have around.

Some BT devices simply will not connect at startup if you have FileVault enabled. This is the case with my Logitech MX keyboard. (I think it's the "low-energy" BT driver that fails to mount, since older keyboards and mice will connect.)

I keep a wired keyboard under my desk, to use when re-booting - and try not to re-boot unless it's actually necessary.

My Mac is an M1 Mini, and draws next to no power when it's idle, so leaving it on is not an issue. If you have an Intel Mac, you can save energy by letting it go to sleep, or putting it to sleep (Apple menu) when you're done using it, so as to minimize the re-booting routine.

Sign into your Mac using your Mac password that you created. This may be different from your Apple ID password.

If you forgot your Mac login password: https://support.apple.com/en-us/HT202860

Connect the charging cable helps to use wireless magic keyboard if bluetooth has gone OFF