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You may have noticed that all the posts and all the comments on this site have buttons to vote them up or down, and all the users have "karma" scores which come from the sum of all their comments and posts. Try not to take this too personally. Voting is used mainly to get the most useful comments up to the top of the page where people can see them. It may be difficult to contribute substantially to ongoing conversations when you've just gotten here, and you may even see some of your comments get voted down. Don't be discouraged by this; it happened to many of us. If you've any questions about karma or voting, please feel free to ask here.
If you've come to Less Wrong to teach us about a particular topic, this thread would be a great place to start the conversation, especially until you've worked up enough karma for a top level post. By posting here, and checking the responses, you'll probably get a good read on what, if anything, has already been said here on that topic, what's widely understood and what you might still need to take some time explaining.
A note for theists: you will find LW overtly atheist. We are happy to have you participating but please be aware that other commenters are likely to treat religion as an open-and-shut case. This isn't groupthink; we really, truly have given full consideration to theistic claims and found them to be false. If you'd like to know how we came to this conclusion you may find these related posts a good starting point.
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Welcome to Less Wrong, and we look forward to hearing from you throughout the site.
(Note from MBlume: though my name is at the top of this page, the wording in various parts of the welcome message owes a debt to other LWers who've helped me considerably in working the kinks out)