Unfortunately, you can't just search for Christmas music from there. The trick is to click to add a new station, and that will give you the search box. I just asked for Christmas, and a bunch of stations popped up. Select one, then click on it to play.
I tried a few stations, and am still trying to make up my mind. Right now I'm listening to Holiday Hits - Christmas and it seems to be OK. By the way, remember that this is radio, so there will be some advertising. In addition, each song will allow you to buy it, or the album, while it's playing.
By the way, I keep my iPad plugged in on my dining room table. That way it can play without my having to worry about charging the battery.