A good way to see mindfulness is as a game.
There are two players: You and your mind.
The aim of the game for you is to keep your attention on the now, on the experience that is happening now. That can be anything. The feeling of your feet striking the ground as you walk, the sound of a person speaking and the meaning of the words they say, the heat of the sun on your face in summer, the cold sting of air rushing through your nostrils in winter, the taste of your dinner or the smell of poo.
All you have to do is stay with the now.
The aim of the game for your mind is to distract you.
It does this by producing daydreams – such as imagining you are a superhero, or imagining you are engaged in coitus. It does it by producing thoughts about what will be done tomorrow – plans (of course you have to plan sometimes but planning is not playing the game of mindfulness), anticipations, worries etc. It does it by producing thoughts of the past – rehearsing old arguments (intellectual and domestic have the same value in the mindfulness game), old scenes, conversations, failures and successes.
The unifying theme of all these distractions is that they are all things that are not happening now.
When you are present, when you are focusing on what is happening now you are winning.
When you are not focusing on what is happening now you are losing.
It is at the moment when you realize you are not focusing on what is happening now that a tug of war occurs between the mind and you. Fixing your attention on what is happening now is harder or easier depending on how fun or stimulating the distraction the mind throws up is. As you play the game more you will get better at it. A result of the game is that you become happier and more peaceful in much the same way as running races or playing football makes you fitter and healthier.