It's not a simple question, even though it may seem so.
Need Quantum Physics to explain actually
So light particles/waves(they're both) only travel straightforward in homogeneous matter, once it hits heterogeneous surfaces, it can be delayed, broken, or reflected.
Everything you can see that does not directly produce light, you are only able to see, because light is being reflected all around you.
So the light will bounce off walls, trees, houses, whatever. This reflection happens, even though you cannot necessarily see yourself in it,
but there technically are mirrors all around you.
If you're asking why you can see yourself in some surfaces: this has to do with the smoothness of the surface the light hits,
the smoother the surface, the more clear the picture of yourself. This is also why water reflects so well