http://ycombinator.com/newswelcome.html
gives an overview of the community experiment here, summarizing the site guidelines.
http://ycombinator.com/newsguidelines.html
The Hacker News FAQ
http://ycombinator.com/newsfaq.html
gives some additional details about how Hacker News is administered. The welcome message distills the basic rules into a simple statement: "Essentially there are two rules here: don't post or upvote crap links, and don't be rude or dumb in comment threads."
I should note that previously expressed community consensus, in a thread someone opened about what kinds of submissions to upvote and what kinds to NOT upvote, revealed that most of the long-time posters here with high karma STRONGLY disfavor links about electoral politics (of any country) or basically political issues (as contrasted with scientific or economic issues). Since I read that thread, I have had a strong tendency to flag as off-topic any new submissions that seem to be mostly about politics rather than submissions that gratify "one's intellectual curiosity" in the sense intended in the site guidelines.
"Why don't I see down arrows?
There are no down arrows on submissions. They only appear on comments after users reach a certain karma threshold."