You must have observed that when our hand comes in contact with fire, it spontaneously retracts away from the fire,
When someone blows air to our eyes, we close the eyes.
In all these happenings, our body responds to stimuli unknowingly, like we are programmed to behave like this.
This spontaneous response of our body to external stimuli is Reflex Action.
Now let us talk about other things which require a conscious mind.
For eating, we pick our food and bring it to mouth.
To buy some grocery we walk out of home by legs and visit grocery shop.
Here we decide the action consciously and do the action to get the desired result. These are called voluntary activities.
Thus walking in the question is a voluntary activity.
How reflex action work
Our body contains numerous sensory nerves receptor, for example, Heat receptor, cold receptor, pressure receptors etc.
External stimuli activate these receptors. These signal move to the spinal cord. Spinal cord in return sends motor impulses to the muscle which result in action.
How walking work
We walk whenever we need them, like jogging, going outside to purchase from a store, play sport, etc.
In such action, our brain analyses the needs to decide the response and send the final signal to concerned muscles, i.e., leg muscle. Leg muscle contracts and relaxes, our hand swings.
Now let us see the inferences: