If you are reading this, the light from your computer or mobile is reaching into your eyes. The cornea and lens of your eyes will focus it on your retina. Light-sensitive cells in your retina produce neuronal signals which are carried to your brain via the optic nerve. This is a result of the neuron's ability to generate an action potential and nerve impulse due to a positive feedback reaction in its membrane.

Your mind interprets this signal or an image if you will, that it has now, as a recognizable pattern because you have an earlier memory of recognizing a pattern. The interpretation, at this level, is a text, from which you derive meaning because your brain is conceptual and cognitive.

When the meaning is understood, a cascade of things occurs. This information will be stored in your short-term memory, which may or may not becomes a long-term memory. Networking between various anatomical regions of your brain such as the hippocampus, amygdale, etc are involved in this process. 

A response to this information can be cognitive, that is, if you decide to think about it and/or/if you decide to write a comment, and also mechanical even if you chose to scroll down or swipe back. The neuronal response from the brain's motor area passes to efferent motor nerves which innervate the skeletal muscle tissues, which in turn contract and relax voluntarily to produce movement in your fingers and hands coordinated by your cerebellum.