Textures are able to add realism to an object by allowing fine detail to be applied to the object's surface; this could be an image of bricks for a wall or a person's face displayed on the character. When a texture is used by the shader, it can often be rescaled and reflection can be added to it; some shaders even allow you to apply surface detail.
We can apply multiple textures to an object to combine them and produce different effects; it will be up to the shader to determine how they are applied.
