ELI5 How does Reddit work from a user's perspective?

I am not able to comprehend some aspects of Reddit.

I understand Reddit is for posting links/matter and voting/commenting.

There are 3 major streams - normal, new and trending. Everything gets posted to new first, gets voted, goes to trending and finally with enough steam rises up to the regular view.

[Need correction / explanation here]

Comments - I use Red Reader Beta from f-droid.org for Reddit. Sometimes I feel the whole comments section is nested and messed up.