I actually have a really good ELI5 explanation for this that I will copy from an older comment. Should help!

The first thing is to imagine being alone in deep space, there is nothing there except you and your space ship. Now imagine having another ship pass you at near the speed of light, the other ship also has only you for a reference frame.

So which one is moving?

To people in the other rocket, who also have no reference frame aside from you, they are sitting still and you just flew by them at relativistic speeds. Movement only exists when measured in relation to another object. Without a reference point, what is moving?

The next thing you have to know is that the speed of light is constant. It moves with the same velocity, with or without a reference point, and that speed is the maximum speed limit in the universe.

Here's a link to visual aids for an old thought experiment about time dilation. The argument is in the space ship situation again. If you had a light source in your space ship that started at the floor and hit a mirror on the ceiling then bounced back down to the floor, to you it looks like it goes up and then straight back down. But the rocket that apparently "moves" past you will see something else. Since to them, it looks like you are moving, what they will see is that the light goes up, but also goes sideways along with the motion of the rocket. Then it goes down again, but again it goes sideways as well. So to them the light beam traveled farther than it did to you. But the speed of light is constant, so in your frame of reference it took a given amount of time to go up then down, but in their frame of reference it took exactly the same amount of time to travel a longer distance.

So there is length contraction with velocity. But also a time dilation. Since light can only move at one speed, it can't travel a different distance without forcing a change in the way time would be measured in each reference frame.

Because of relativity a photon does not experience time. One consequence of relativity is that time slows down as velocity increases relative to an observer (called time dilation). When a photon leaves the sun, in our frame of reference it takes a few minutes to get here. But since the photon travels at the speed of light, the time dilation is infinite, this goes along with another relativistic effect which is length contraction at relativistic speeds. The length contraction is also infinite at the speed of light. So to us it takes the photon some time to reach us from the sun, but to the photon it is instantaneous. It crosses no distance and experiences no time.