<human>: Hello everyone!

My boyfriend has invited me to his family's Christmas this year, which is sort of a whatever for me, seeing as I celebrate in January. He is very pro-Christmas, it's his favourite holiday, but the way I've always celebrated, er, Ukrainian Christmas(?) is very different from the Christmases I've seen in some movies.

I really want this to be special for him and his family. His mother has been asking for gift ideas for him and I have no problem in the gift part, but I don't want to come off as weird or not-knowledgable about the season. Really, I don't know any traditions. I don't get why there are socks on the wall? Why are we eating meat? Why aren't we spending the whole day in church and eating at the first star? 

I get why, obviously. My question is more what do I do to keep from being rude/embarrassing myself/being part of some Christmas faux pas? What is the thing people kiss under? Why do they do that? Do I have to drink eggnog? Do I give a gift for the family at Christmas? Does everyone get a bunch of gifts from me? How much wine am I allowed to drink when my boyfriend starts singing? 

Most importantly: they come from a very sheltered small town which is mostly white, mostly Protestant, and quite Anglo-Saxon. They are from a small town on an island. What's the shortest and most no-nonsense way to explain to them that I don't celebrate Christmas without it completely erasing the fact that I do, just not their way?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Ukrainian Catholic twenty-something does not want to make an ass of herself at her first Christmas with her boyfriend's family. What do? What not do?