You said:
That'll get the job done. The 8 note is the root note one octave higher. So playing R-R-8-8 and changing roots as the chord progression moves to new chords is a start. When that gets easy add the 5, (R-5-8-5) for a little more interest (look where the 5 is, yep right below the 8). Now that will play a lot of bass, probably take you where you want for the next year.
When that gets easy throw in the correct 3 (R-3-5-8) for major chords (C) or b3 (R-b3-5-8) for minor chords (Cm). You get the b3 by moving back toward the nut (tuning knobs) one fret - a #5 would be telling you to move one fret toward the sound hole. You'll need to look at this for the light bulb to come on.
Chord Formulas
Take it one step at a time you eat this elephant one bite at a time. See if the keys will have the chord names, is he playing from fake chord or basic piano sheet music. If piano sheet music, I bet he could tell you what chords are being played and when in the song. With out that - good luck. You gotta know that to change chords when the song moves on to new chords.
Here is a plate full of stuff that may help. Eat as much as you need to satisfy your hunger, but, not enough to make you sick.
Take the box pattern and place the root note (name of the chord / name of the scale) on your fretboard and the intervals of that pattern are always in the same place - on your fretboard. So if you want something else besides the root note, like R-3-5-3 you can find where those notes are.
Bass Patterns based upon the Major Scale box.
Code:
Major Scale Box.
G|---2---|-------|---3---|---4---| 1st string
D|---6---|-------|---7---|---8---|
A|---3---|---4---|-------|---5---|
E|-------|---R---|-------|---2---|4th string
Place the root (R) on the C note 4th string 8th fret and the C major scale await you.
Place the root (R) on the C note and play the R-3-5 and you have just played the notes of the C major chord aka C arpeggio. Chord progression for this song is G-C-D. Place your box root on a G on the 3rd string. Where is your C? Where is the D? The next song's progression is C-F-G. Place your box root on a C on the 3rd string. Where is your F? Where is your G? Yep, piece of cake.
The rest of the story - more than you need right now, but good information to have. Think of it as stuff in the freezer that you could get if you need it.
Basic Chords
Major Triad = R-3-5
Minor Triad = R-b3-5
Diminished Chord = R-b3-b5
7th Chords
Maj7 = R-3-5-7
Minor 7 = R-b3-5-b7
Dominant 7 = R-3-5-b7
½ diminished = R-b3-b5-b7
Full diminished = R-b3-b5-bb7 Harmonic minor and melodic minor will use the full bb7
Scales
Major Pentatonic = R-2-3-5-6
Minor Pentatonic = R-b3-4-5-b7
Blues = R-b3-4-b5-5-b7
Major Scale = R-2-3-4-5-6-7
Natural Minor Scale = R-2-b3-4-5-b6-b7
Harmonic Minor Scale = R-2-b3-4-5-b6-7
Melodic Minor Scale = R-2-b3-4-5-6-7
Have fun.
). I started by just playing the first note of the chord then just some of the notes in the chord to give it a little movement. very basic, but it's start. 
I set this up just to show you, kunji.
