Let it C
This is a good starter strumming tune, even though the recording is piano.
Make the connections. Sing the words [just to make sure: change the ‘C’ to ‘Be’ in Let it ‘C’], or just the melody in la-la-la.
Strum along to the recording.
A chord scale is playing chords in alpha-order, as we commonly play single tone scales. Playing chord scales is a primary practice. It tunes our ears to what is inside of a key. It provides the base chords for any key. It creates a solid starter set for figuring out songs or harmonizing melodies.
Start on lowest root, play to highest, then to lowest, then back to the root. The key of G has one sharp...F♯. So, it is one tone different than C Major [all of the Fs have been "moved" to F♯s]. Get this scale in the hands...train. Then jam a bit with it. Next, we will learn the chords which come from this scale.
Play the power chord exercise as written. Say the root name as you play each for 4 beats. Make sense of the naturally occurring half steps. Memorize names for each position.