One way to think about all this is to think of a bouncing ball. If you bounce the ball off a rough surface, like a stone wall, there's no pattern to how it will bounce and where it will bounce back to. But if you bounce if off a smooth surface, like a tennis backboard or a basketball floor, you can predict at what angle the ball will bounce. The same is true about photons hitting a surface. Now photons are different from bouncing balls in at least one very important way.
Some surfaces can actually absorb light.
That s why not all smooth surfaces will reflect your image. But you're probably still wondering what this has to do with seeing something in the mirror, like yourself, for you're probably thinking you don't produce light. But even objects that don't produce light are bombarded by it. And just like any other rough surface, the light bounces off of us in every which way. But when you stand in front of a mirror, some of the photons bouncing off you will hit the mirror.