Why don't you try what's being suggested to you first?
Do this:
1. Connect backup drive with CCC clone on it
2. Press the power-on button
3. IMMEDIATELY hold down the option key, and KEEP HOLDING IT DOWN
4. In a few moments, the Startup Manager should appear
5. If your CCC backup drive is bootable, you should see it listed in the startup manager. Select the backup drive with the pointer or tab keys, then hit return.
What happens next?