Question about a swingers party?

My girlfriend and I were invited to a house one, and are planning on attending out of pure curiosity. and for the sake of trying something new. I'm really not sure what to expect or how one even begins, gives me the butterflies expecting the unexpected. Is there something that I should be doing? Do couples usually chat up and mingle.. is there asking involved? Or is sexual contact expected when attending one. We do want to mingle with others, but do not at all want to feel pressured, nor do we want to be the lone weirdos sitting there doing nothing. Just a lot of thinking, anyone have any experience and feel like lending a noob some advice?