In Lesson One the root note is defined as being the letter note of each chord, e.g., Am - root note A; G7 - root note G.
For this step of the arrangement, write down the root note (in the bass) on the first beat of each bar. Be sure to hold each bass note for its full value of 3 counts.
This step of the arrangement illustrates an example of two part writing. Other examples of two part writing can be found in the Supplementary Pieces Section (e.g., Silent Night, The First Noel, etc.)