Welcome. I'm sorry that you are in such an awkward situation with you family. In terms of dealing with this conference, I can only echo what MixedNuts said (except for the panicking part). I've always found this quote interesting:
Adulthood isn't an award they'll give you for being a good child. You can waste . . . years, trying to get someone to give that respect to you, as though it were a sort of promotion or raise in pay. If only you do enough, if only you are good enough. No. You have to just . . . take it. Give it to yourself, I suppose. Say, I'm sorry you feel like that, and walk away. But that's hard
We have every reason to think that children's beliefs have no momentum - the evidence is right in front of us, they change their minds so often for such terrible reasons. By contrast, the fact that I disagree with another adult is not particular strong evidence that the other person is wrong.
In other words, try to free yourself from feeling obligated to defend anything or feeling guilty for not engaging with those who wish to change your beliefs. You might consider explicitly saying "Social pressure is not evidence that you are right (or wrong)." If the people talking with you assert that they aren't using social pressure, then ask them to stop continuing the debate. Their willingness to leave is a victory for your emotional state, and their refusal is strong evidence that arriving at true beliefs is not really their goal - but the proper reaction to that stance is to leaving the conversation yourself, not try to win the "you are being rude" debate.
In short, maximizing your positive emotional state doesn't rely on winning debates. Your goal should be to avoid having them at all. (If you hadn't already read the book your father found, I would have suggested declining to do so).
A few notes about the site mechanics
A few notes about the community
If English is not your first language, don't let that make you afraid to post or comment. You can get English help on Discussion- or Main-level posts by sending a PM to one of the following users (use the "send message" link on the upper right of their user page). Either put the text of the post in the PM, or just say that you'd like English help and you'll get a response with an email address.
* Normal_Anomaly
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A note for theists: you will find the Less Wrong community to be predominantly atheist, though not completely so, and most of us are genuinely respectful of religious people who keep the usual community norms. It's worth saying that we might think religion is off-topic in some places where you think it's on-topic, so be thoughtful about where and how you start explicitly talking about it; some of us are happy to talk about religion, some of us aren't interested. Bear in mind that many of us really, truly have given full consideration to theistic claims and found them to be false, so starting with the most common arguments is pretty likely just to annoy people. Anyhow, it's absolutely OK to mention that you're religious in your welcome post and to invite a discussion there.
A list of some posts that are pretty awesome
I recommend the major sequences to everybody, but I realize how daunting they look at first. So for purposes of immediate gratification, the following posts are particularly interesting/illuminating/provocative and don't require any previous reading:
More suggestions are welcome! Or just check out the top-rated posts from the history of Less Wrong. Most posts at +50 or more are well worth your time.
Welcome to Less Wrong, and we look forward to hearing from you throughout the site.
(Note from orthonormal: MBlume and other contributors wrote the original version of this welcome message, and I've stolen heavily from it.)