The lens of the eye casts an upside down imagine onto our retina and then our brains take these two upside down images at slightly different perspectives (one per eye) and creates a single right-side up image.
With that said, you probably won’t be surprised to hear that processing visual information takes a lot of our brains’ processing power.
To get a full explainer of how our eyes work, check out the video below.
FACT: We also see the world flat, but the two offset images we see and the light and shadowing allow us to perceive depth. So yeah, we see two upside down flat images that are slightly off from each other and the brain turns that into something useful. Very cool brain.
The Visual System: How Your Eyes Work.