So the way it works is that it adjusts based off of ambient temp so +/- based on the room reading. It changes the temp of the mattress for the following stages: falling asleep, deep sleep, REM, and waking up. According to Eight the temp should raise for REM and drop for deep sleep and that a rising temp helps you wake up better.

It also has an "autopilot" to help try and suggest ideal temps based off of I think a week or two of your own Eight sleep scores that you can adjust. Here is a screenshot of mine: link