A mode is just a scale that comes from another scale (probably one you already know). Triads, arpeggios, and chords are built from these modes and that right there is the foundation for a thousand bass lines.
This video lesson follows on from a lesson I recently recorded that I recommend you watch first:
Scroll down for the backing track and PDF downloads.
I Will Survive Bass Guitar Backing Track
Triad and Mode Bass Guitar Diagrams
These are the shapes and patterns you need to know but, first, the chord progression the lesson is based on is I Will Survive.
These are the modes you can use over the chord progression.
Arpeggios (and triads) are formed from the modes.
Don't worry if this fries your brain a little bit. It's well worth persevering with as the amount of creative ammunition it will give you is astonishing.
Remember though that you don't need to use all these ideas! Often, roots, fifths, and octaves sound perfect. Played with impeccable groove and timing, you don't need to play all the notes available to you. Ultimately note choice is down to taste and that's down to your creativity.
Keep playing, keep practising and you will gain more command over your bass playing.