Question

How can the universe expand?

Answer 1

It just does. Its not a matter of how can the universe expand, but why the universe exists.

Explanation:

The universe expands faster the the speed of light, but its not the movement of matter but rather the increasing distance between matter (this can be clumps of it, galaxies of it, star systems of it, etc), but what caused this will allow use to see why it can expand without having any physicality which we can observe.

Hope this helps! (or possibly confuses you more)
-C. Palmer