Set up my desktop and my magic mouse

If you cannot make a connection, first ensure the keyboard and mouse are turned on. If they are and you cannot setup then use the following instructions to setup the BT keyboard and mouse:

The following will require any USB keyboard and mouse. If you don’t have them, borrow or buy them, they are inexpensive!

1.     Connect the USB keyboard and mouse to the computer.

2.     Open System Preferences – Bluetooth

3.     Un-pair the wireless keyboard and mouse.

4.     Turn off Bluetooth

5.     Restart the computer in Safe Mode per the directions in Use safe mode on your Mac - Apple Support

6.     Restart the computer normally.

7.     Open System Preferences – Bluetooth

8.     Turn on Bluetooth

9.     Re-Pair the wireless keyboard and mouse.

10.  Unplug the USB keyboard and mouse and begin testing the wireless devices again. 

If you cannot figure out your password, then follow the directions for If you forgot your Mac login password.

Finally, if you are hopelessly lost just give AppleCare a phone call. To find the number for your country please click AppleCare Contact Info

Which exact make & model is your computer? Most likely, it will have USB-A type ports. Just the very latest models have USB-C ports. Regardless, any brand wired (USB-A) mouse & keyboard should work for this.

Something like these: https://www.amazon.com/Logitech-Full-Size-Keyboard-High-Definition-Optical/dp/B003NR874S/ref=sr_1_5?crid=1OONXA951K8PO&keywords=wired+keyboard+and+mouse&qid=1706061252&sprefix=wired+keyboard%2Caps%2C1027&sr=8-5