This system of interpreting music has a very handy visual method of showing rhythms. All the chords are broken down into measures. When you look at a chart, you can see exactly where the chord occurs. Each chord gets its own measure, and usually they are written with four measures per line. Additional rhythmic markings can occur, but for this example, the chords will be evenly spaced so as to be easily recognizable.
I've included two classic Christmas charts for you to practice on. Its not important to embellish the changes just yet. This lesson is aimed at getting you to a level where you're comfortable in a situation where accompaniment is needed quickly. The first and easiest chart that I've included is Irving Berlin's classic, "White Christmas". The chord in the first measure is held for four beats, and in the second measure, each chord receives 1 beat. In this scenario, assume there are four beats that occur between every line. Use the chords correspondingly.
The second chart by Mel Torme is a bit more complex. You begin to see some of the aspects that we talked about earlier. You will encounter things such as extensions (7ths) , chords with accidentals, and inversions. This is where a drum loop comes in handy. Once you get a good groove going, share your newly acquired Christmas repertoire with family and friends. Enjoy the holiday season!