How much percent of image does our eyes focus at any instant?

What you learned in high school isn't exactly true (or is misremembered). Human eyes get visual input across about 120 degrees of visual angle, and some herbivore mammals see near 360 degrees total between their two eyes.

However, the resolution is not constant. The fovea is an area of high-density receptors in the retina. When you look at something specific, you are directing light from that area of the visual field to the fovea. The fovea is limited to about 2 degrees of visual angle.

Additionally, your attention is often limited to a small section of the visual field. When viewing a scene, your eyes will naturally make saccades to bring various points into high acuity vision to get a good sense of the entire scene, but you are still seeing all the surrounding area, even if you aren't paying much attention to it. Importantly, you are still sensitive to surprising stimuli (especially those that are high-contrast or moving) in those areas that might cause you to redirect your attention, otherwise you would be very easy to sneak up on.