1. Imagine you're doing a song in the key of A and that you want to transition from A to D on your progress. To do walking bass line like that, you can play A, B, C, C-sharp to D.
2. Back to play a D, down to F-sharp, the strings E, G, G sharp and return to A. This original comes from the underside of the scale that you approached the A of the lower notes.
3. Enter together and noticed that you use four fingers to do this. This way you're keeping the same radius frets to get from A to D. This creates a clear voice. Do not try to play each note with one finger because it will make it more difficult.