how do i find the machine ID number on my computer?

Open System Profiler in your Utilities folder. It's in the opening panel.

Do you mean the serial number, the model number, or something else?

 Menu > About this Mac. Doulble click the OS Version number.

That's the serial number, but not the model/machine ID. The latter looks like this:

It is not displayed in About This Mac. You need to use the System Profiler.

Ah!