Welcome to steemit. Try this link first: https://steemit.com/steemit/@vimukthi/a-philosophical-and-economic-outlook-at-steemit-sbd-and-flagging-and-suggestions-for-a-better-future-based-on-positive

Hopefully it's not overwhelming. You downvote someone with the flag button on the upper right corner of the post. There are some big flagging wars going on steemit. Don't think too much about them. Take it slow. At the current state a flag is the opposite of a downvote. The only difference is that when you get upvoted, each vote improves your reputation. But when you are flagged(downvoted) your reputation only goes down if the person flagging you has a higher reputation than you.

I'll also drop some other helpful links:
https://steemit.com/faq.html
https://steemd.com
https://steemworld.org/@steemchiller
https://coffeesource.net/