For example, while we eat, we get all kinds of thoughts, and we can easily get lost in them. Planning about the future, thinking about the past. We can get lost in our mind and our thoughts carry us around.
This is our default mode.
With meditation, we can learn to focus on what we are doing much more precisely than "typical" focus that we think is focusing, but the typical one we consider mainly "what we think our body is actively doing". We do not typically consider what's going on in the mind.
With meditation, we can learn to let go of the thoughts in our mind, so that we do not get dragged around this way or that way easily.
Training the mind is a skill that one learns over months and years.
When I meditate, I deliberately let the thoughts pass, and every session of meditation trains me to automatically be able to do it during my daily activities.
So when I am eating, I am only eating, with my body, but also my mind. When I am relaxing, I am truly relaxing. When I am thinking about something, I am truly thinking about only that thing.