Discuss why the article says the fact that we're in our universe complicates our understanding of the expansion of the universe.

It means that that being in just one universe makes it harder to grasp it's expansion

Because of our perception of the universe from inside the universe, we are unable to see how and towards what the universe is expanding. Also, our understanding of it is further complicated because we are moving as part of the expansion, thus distorting our perception of it.