Mindfulness is being fully aware of what you are doing, feeling, or thinking in the present moment, while calmly acknowledging and accepting one's feelings, thoughts, and bodily sensations without judging.
Mindfulness is used as a therapeutic technique that can be used in leading to happiness and overall well-being.
When your mind drifts away, it is bringing the mind, back to the body and just noticing what you are doing or what is going on in the moment. It is a form of meditation and concentration but you can do it anytime not just when you are sitting for meditation. When you do something with awareness whether you are working, simply just walking, eating or other activities doing it with mindful attention on your self.
Mindfulness involves a conscious direction of our awareness toward your activity in the moment. If you are eating it is consciously being aware of the process of eating. Eating with purpose and awareness. Noticing the taste and aroma of the food that you are putting in your mouth as opposed to watching TV or reading and mindlessly shoveling food into your mouth.
Purposefulness is a very important part of mindfulness. Having the purpose of staying with our experience, whether it's the breath, or a particular emotion, or something as simple as breathing, means that we are actively shaping the mind.
When you are mindful of what is happening in the present moment for a certain amount of time, it creates concentration. When your concentration is strong enough, it leads to insight or wisdom that helps you to overcome difficulties and generate more joy and happiness in your daily life.
To benefit from mindfulness you need to practice it. Practice bringing the mind back to the body to the present moment to be present with your actions and learning to be your true self.