How can I lock and recover my stolen Mac?

Since you didn't enable "Find my Mac" prior to your notebook being stolen, you will not be able to use any of the recovery features that this option offers, as Lanny has already pointed out.

At this point, the first thing you should do is change your Apple ID password, and then, contact your local law enforcement agency to report the theft.

You can't, without Find My Mac being enabled.

Even if it was enabled, the chances of recovery would be slim to none. If the stolen Mac was powered on and connected to the Internet, you would have a chance to lock it or erase it.

The best way to prevent theft is to never let it out of your sight.