FebChallenge Day 19: Low Key, High Key

I was unsure about this technique so had to do some quick reading up on it. I'm still not sure if I've done it right. Do I need to layer images? One under, one over and one correct exposure?

I wasn't sure so took this well over exposed image and ramped up the contrast. Any hints as to how to do this technique properly?

The subject is a Be@rbrick (mentioned on the Toys challenge)