The closer something moves to our universes maximum speed limit (The speed of causality(the speed of light)) the slower time goes for it. We call the fastest speed speed of light, but it has actually got little to do with light itself the way people might think of it. It just happens to be moving at the fastest possible speed and it is everywhere so we have started calling the maximum possible speed the speed of light.

So yea.. the faster something goes near the maximum speed the slower their clocks tick. But also nothing with mass can actually reach the speed of light, since the faster you move the more mass you gain - e=mc2, the more mass you gain the more energy you need to push further etc etc. So things with mass could never achieve it.

However photons are massless particles, they have no mass. (Except in some sense they do, again because of e=mc2) and since they have no mass they move at the speed of light. If you have no mass you move at the speed of light by default. Hope this helps! Its a fascinating topic.. as our entire universe is.