In the United States, the holidays are set during the month of December and January; students will usually get up to three weeks of break (The winter break) to spend with their host families.
The Holidays include Christmas and new year; and if you come from a country which these traditions aren't a big of a thing, you are in for a good fun!
Christmas is the Christian celebration of the birth of Christ, which is held on the 25th of December; many of you will have heard or even celebrated this before, but here are some information - tips.
During this time, you are expected to be spending time with the family, to show your gratitude and just to be polite; you can help them prepare the place for get-togethers (If your family is hosting one), and just spend time with them during this time. it's not really a must, but it will greatly improve your relationship with them. You would also want to prepare some gift for each of the family members, preferably something native of your country. (again; it's not a must, but you totally should do it!) I brought some gifts from my country and I could tell ya, it was the best feeling to see their faces when they open it!
the second holiday held during this time is the New Year; it practically is just celebrating the new year (duh).
You can choose to either stay with your family, or you can go to parties with friends; but be very cautious and not too have too much fun that might get you in trouble. I choose to go hang with my friends for a countdown - games; it was a very great time; made new friends, get to hang with best friends, etc.
You may also go through some home-sickness during this time; just make sure to spend quality time with your host family, and find something that would occupy your time. It's not easy being an ocean away from your family, but you must try not to contact them too much; that could worsen the situation!