This is a counting practice that's great for giving the mind "something to do" while building the strength of the observing part of our mind (opposite to autopilot). It is recommended that you start with a body scan in Neil's courses, though it really doesnt matter if you prefer this one first.
Mindfulness is about being able to focus on one thing with awareness for extended periods. Mindfulness practice is life-changing, so start making it your habit!