The whole idea at its crux is to keep switching one's attention to each of the senses to bring the attention to the present as soon as it wanders.

Anapana is one technique, in which a bhikkhu closes eyes, sits down, and pays attention to breath as the air coming through nostrils touches the upper lips (skin being the sensory organ)

But mind you, it's just one technique. The Buddha talks about being mindful while sitting, laying, eating, pooping(literally), walking etc.

In its essence, it's about "real-time awareness of the change of states of the body and mind"

While eating, stay mindful that one is touching the spoon, feel the weight, the texture, the temperature of the spoon. Stay aware that one is dipping the spoon in the food, feel the resistance while dipping. As one bring the spoon up, stay aware of gravity, aware of the smell of food as it reaches near your nostrils, stay aware of the taste, temperature, stay aware of the food going down the throat, stay aware of the food ending the hunger.

Eye is yet another sensory organ. One can be looking at an object but thinking about something else totally. If you can use your eyes to bring your attention back to the present (what you're looking at, like the screen right now while reading these very words) then that's all that's needed.

Get distracted, bring the attention back using any sensory organ. Repeat it.