How can something travel faster than light?

Answer: Light slows down when going through water or air or gas. It's only in a vacuum that light travels at 'c' (from Einstein's equation). And it's that speed c that is a limit due to relativity.

But the exciting thing is that when you're not in a vacuum particles can be traveling faster than the local speed of light (maybe 75% c). And that process of a particle zipping along gives off Cherenkov radiation.

I think of it as the light equivalent of a supersonic shockwave and sonic boom. Faster than sound gives noise. Faster than light gives light (or other electro magnetic radiation)

(People with more knowledge might say the sonic boom analogy is very inaccurate but not sure)