What you practice and repeat becomes Habit. The Habit Loop is a concept to help you become aware of your habit, providing you the opportunity to change it.
Awareness is the first step. Do you have a not-so-healthy habit you want to change? First investigate the habit. Identify the Trigger, the Routine and the Reward. But, really take extra time to discover what "reward" you are getting or trying to get.
It's possible there is another or new routine you can swap out to get the same (or even improved) reward.
Here's an example:
Tigger: Eat Lunch
Routine: Eat a piece of chocolate
Reward: Energy for the afternoon
What else can bring you energy? Maybe going outside for some air, sun and a few steps?
Change the Routine:
Tigger: Eat Lunch
Routine: Go outside for some air, sun and a few steps
Reward: Energy for the afternoon
It takes time, thoughtfulness, commitment and patience.
Check out this video for more details: The Habit Loop
