Harmonise a scale into modes, triads, arpeggios, and chords and you have everything you need to make a life time's worth of music. That's no exaggeration. This stuff is very much in the lightbulb moment category so watch this lesson over and over again until you understand!
The scale used in the video is relative to C Major. I did a video lesson on that one too so you may want to watch that here. Scroll down for the free PDF. Remember you can (and should) transpose this to the other 11 keys.
The whole idea behind this is to know a scale. Once you do that, you can create (VERY easily) a triad, arpeggio, and chord. Those are the building blocks of music and of bass lines. Learn these components, listen to music to hear how the best musicians have used them, and you'll be well on the way to mastering this.