What and why? (If I can finish in this much only then why to write so long?)

I was just upgrading my pentesting tools and saw the network activity.
Files were being downloaded but something was being uploaded too.
(This is not the first time I saw this kind of thing, just the curiousity came now!)
What is the thing that was being uploaded and why???
(Maybe I used too much “being” ! Did I???)

Note:- I am not a hacker or something so please don’t ask about this, just learning it! Pleaj!!!