first u gotta know your scales.
as for walking bass, try learning some jazz. it'll help you alot!
However if you are refering to church music, it's usually passing notes. Or, in scores, "compound" chords like G/B and Am/C
They will sound like walking basslines because it is commonly used in this progression:
G D/F# Em
see the bass walking downward while the chords are changing? cool eh?
hope that helps.