To me the mind has 2 things that it can focus on. It can either "experience of the moment" as sensed by the senses or "think about the past or future" what could happen, what if I had done something different etc

Experience of the moment is sometimes called mindfullness

Mindfullness is a direct engagement with the world as it's being presented to your senses, without much conceptual filtering.

Notice your surroundings

Don't multitask

Thinking about the future is sometimes referred to as Conceptual thought

Conceptual thought involves memory, planning, imagination and abstract reasoning. You're using concepts and memories to construct mental representations of things that aren't physically present.

Both mindfull thought and conceptual thinking are essential for our wellbeing. However modern life seems to unbalance these modes of thinking, leading us to engage in far more conceptual thought than mindfull thought. This can be very stressful. Walking presents us with a chance to redress that balance if we can focus on our surroundings and refrane from multitasking while we walk