I would like to read the 3 paragraphs what I can do now after having achieved 3000+ reputation. I was offered to read them as I reached 3k rep, but now I cannot find it.
If it's not too long ago, you can just open your achievements dialog (the trophy in the navigation bar) and click the notification about the new privilege:
This will take you to the link @DanielFischer provided in the comments: cast close and reopen votes. @T.S' link (also accessible from the 'privileges' link in the top of the achievements dialog) is helpful if you want to see all privileges you earned/can earn.
In general, to check what one can do with certain amount of "reputations", see this page in the help center: