This clip demonstrates how an A-B bass line works. An A-B bass line is where you play a passage and then follow it by something slightly different, the B part, and then back to the A part.
This clip also shows how an A-B bass line works only using Rick James' line in Superfreak.
This song started out as an exercise in arpeggios and then finger tapping and then slapping. During the tapping at the beginning I'm using my left hand to keep a the chords going while I use my right hand to essentially play the melody. Notice in the slapping part how there are two movements one over the top of the other. Part of the line is going down while the other part is going up. It's a neat compositional effect as it adds novility to the bass line without really doing much.
This is a good lesson that shows you how to use your thumb with the #4 (E)and #3 (A) strings. Remember to start slow and build speed. As you play it slowly you are just trying to get your muscle-memory trained. Soon you will be playing it fast and that's when it starts to sound right.
Also note that she is using a thumbs down position for her right hand to slap the strings. This can be played in a thumbs up position as well.