When you look in a mirror, you see a reflection of yourself. Naturally, you expect that image of yourself to appear as it would to anyone standing in front of you looking at you. But that’s not exactly what happens! If you stand in front of a mirror wearing a shirt with letters on it, those letters will appear reversed in the mirror.
The way this bounced light presents an image of you is a bit like the way a piece of paper presents an image of a rubber stamp. Take a look at the bottom of a rubber stamp: if there are words on it, they appear reversed. When you dip the stamp in ink, and press it on paper, the words appear as they should. It’s the same if the stamp is a picture—the picture on the stamp itself is reversed compared to the image on the paper. The paper is like the mirror, and the ink is like the light bouncing off the mirror—it is creating an image of you that is the reverse of what you actually look like.