This is the most simple triad to create. It is a Major Chord. You can use this triad as the basis of creating other chords by altering it on the fly. As a bass player you can concentrate on these notes in a line using other notes in the Major scale as only passing notes. This is not a rule but the simple place to start exploring.
Major Triad: ROOT, M3, P5
This is the 1st, 3rd and 5th of the major scale. It is a simple as that.
For 6 string Guitar and Piano
On keyboard you may invert the chord to M3, P5, ROOT or P5,ROOT,M3 - these would be known as inversions. On guitar you may omit the 3rd in the first octave and play it in the second octave, it is also likely that you will repeat the ROOT and P5 an octave higher.
Things to know:
You will not always represent M3 in the first octave on a guitar or play simultaneous notes including the M3 in lower octaves on a bass. If a chord is being played by another instrument with only the ROOT and P5 the bass can introduce the M3 to emphasize that it is to be a Major - this applies in chord theory wherever a chordal sound is being produce with omitted intervals.