Practice playing chords
Before starting to play these tunes, it would be a good idea to first warm-up playing the exercise at the end of the earlier lesson "Playing intervals and chords in the C position".
The first tune was evidently written for practicing 2nd and 3rd chords (interval counts of 2 and 4 respectively) with the left hand. Here's how it sounds preceded by a warm-up of just playing these chords with the right and left hands (not the same as the warm-up above).
OK. The time has come. You are now going to play a tune that puts together everything you've learned so far PLUS using both hands at the same time! It will take some practice to get both hands coordinated so take it one step at a time.
First become comfortable just playing the right hand, or treble, part of it. Then with the left hand practice switching back and forth between the two chords D-G and C-G. The former is a Major 4th (interval of 5) and the latter a Perfect 5th (interval of 7).
Next, start playing with both hands really, really slowly. Hold those left hand chords for the entire measure (with one exception). Whatever rate (tempo) you use, try to keep it constant. As if you don't know this tune, here it is.
And this is a tune you might actually want to play for family and friends, at Christmas time anyway.