You can find Blink in the Windows Phone Store in the usual way. Once installed, it appears both under the main application menu and also as a 'lens' inside the main Camera application.
The idea is that the application grabbes 16 photos and you choose the best one. Behaviour is actually different, depending how you like to take snaps. If you like using the on-screen icon, the 16 shots are taken right after you tap on the screen to focus (and after focussing itself, obviously), so the system works but you may still be too late for the moment.
However, if using the shutter button, Blink is always taking photos, i.e. continuously after you've half pressed to get a focus lock, but only buffering them in RAM and discarding those from more than a second or so ago. When you press the shutter key, the most recent 8 photos are kept and another 8 are taken, to give you a decent range to choose between.
You then save the one you like best to the Camera Roll. The system is interesting, but there's also the huge restriction that (for speed reasons) the photos are limited to 1 megapixel, which is OK for Facebook but will be of little use to anyone used to taking decent 2013 photos.
There's a direct link within Blink to its own tutorial video, also reproduced below, along with a promo. By all means experiment with Blink, but do use the shutter button and focus before 'the moment'. And comments welcome if you can live with the low resolution.