The pop-out player allows users to click a small icon at the bottom of the screen. Once the pop-out window appears, it can be resized and positioned anywhere on a computer's display.
The pop-out player is designed to stay on top of whatever else you're doing on your computer, and it can be closed by clicking the X in the player, choosing Back to Browse, or closing the Netflix tab. Subtitles are not currently supported in the pop-out browser.
Netflix appears to be testing the feature with a limited number of users at the current time, and Netflix has yet to announce the feature. Netflix did confirm to Engadget that the pop-out player is "only a test" in an image, so it's not clear when and if the player will roll out to additional users.