This was one of the first songs I taught myself as well. Take my advice and don't half-ass it. If you have a good ear, by all means, you can try to learn it that way. However, you can get the songbook here or, if you're more of a beginner, there is a beginner's version. Both are official and I still consider the advanced book one of the best purchases I've made. Christmas Time is Here is a great song, but so is every other song in that book. All of them are a lot of fun to play.
The beginner's book is the one with the red stripe. Some asshole reviewers gave a 1-star review for the book just because they ordered the wrong version. Don't make the same mistake :)