Need Help Running Rescue Boot Disc

I just made a rescue boot disc with Macrium Reflect. The Wannacry prompted me to be better prepared and hopefully restore my computer if necessary from an external HD connected by USB. I have a Thinkpad E570 with Windows 10. I can't figure out the sequence to test the rescue disc. Do I insert the rescue disc when the computer is on and then shut it down? What key do I hit when I start up? If I could get to the right menus I could probably proceed ok. Thanks.

Thanks. I am in need of a step by step to get to what you are telling me to do. I have the boot disc in the CD/DVD drive and Macrium backup of my HD on a HD connected to the computer by USB. Do I need to have the boot disc in my computer before shutting it down. I can't open the CD/DVD drive when the computer if off.

JWalker said:

Thanks. I am in need of a step by step to get to what you are telling me to do. I have the boot disc in the CD/DVD drive and Macrium backup of my HD on a HD connected to the computer by USB. Do I need to have the boot disc in my computer before shutting it down. I can't open the CD/DVD drive when the computer if off.

Specific instructions for Lenovo...
https://support.lenovo.com/gb/en/solutions/ht500207

...in addition to changing the boot order in Bios, apparently there's also a F12 boot device menu available. You have to start from cold to see it, so insert the USB or DVD you want to boot from and use Restart (or turn off fast startup and then shut down).

Thanks so much. I will see if I can navigate through the procedure. It is a dry run at this point.