how do I turn Find My > MacBook on?

First, you need to have an Apple ID and be signed into iCloud on your Mac.

If you need to sign into iCloud, go to System Preferences and click on Apple ID in the upper right of the window.

A new window called Apple ID will open.

In the Apple ID window, in the left column select Overview and sign into iCloud.

Once you are signed into iCloud, still in the same Apple ID window,

In the left column select iCloud.

Then in the right column (heading (Apps on this Mac using iCloud), check Find My Mac.

System Preferences >> Internet Accounts >> iCloud

Refer to picture below