Why we can't see our Sun as it was a few years ago?
Our Sun moves through the galaxy much slower than light does. So the light that was emitted last year by the Sun is already very far away from the Earth. Therefore, we don't receive any light from (i.e. we don't see) the Sun as is was last year. 

As an analogy, image walking along and shooting bullets in all directions. The bullets are going much faster than you can go by walking, so you won't ever get hit by your own bullets. But someone walking next to you can get hit by the bullets you are shooting out.