The Universal Web is a difficult thing to describe, let alone understand. I don't fully understand it myself. Think of it like this. Imagine a spiderweb in the morning, covered in little droplets of dew. Those little dew drops can be thought as being galaxies, and the spiderweb is the net that they formed on. So the Universal Web is basically a large construct of thin, invisible fibers that galaxies form on. What these fibers are made of is still unknown, and how they got here in the first place is an even bigger mystery. All we know is that they're here. So yeah. That's all I know I guess.