| hi marine18!
thanks for checking out that basslines article. the answer to your question is tough to provide you within a single thread because it is quite extensive, but i'll try and cover some basic concepts for you here...
assuming you're talking about playing walking bass in more of a jazz context, it's all about being able to cover two essential roles:
1-being the foundation for the time
2-being the foundation for the harmony
in terms of being responsible for the time feel, it is vitally important that you do A LOT of listening in the idiom, and learn how to identify and understand the level of interaction between all of the players. as a bassist, you have a tremendous responsibility to be on your game and have confidence in your time feel. with walking bass lines, the pulse is every bit as important as complementing the harmony.
being the foundation for the harmony means that it is your responsibility to outline the chord changes; this requires a basic understanding of chord types and colors, as well as the relationship between scales and chords. you also need to have done enough bass line listening and transcribing to have developed a sense for what is appropriate within the idiom. just because you play notes that might theoretically be 'correct' under each progression, it doesn't mean that what you're playing would necessarily be traditional in a jazz setting... so, once again i can't overemphasize the need to do a lot of listening, transcribing, and ear training.
if i am working with a beginner, i generally teach walking bass concepts using a 3-tiered approach in order to provide him/her with an understanding of how these lines are built from the ground-up:
1-using chord tones only
2-adding scale tones
3-adding chromaticisms
i generally begin students with chord tones in order to promote good ear training and chord recognition. arpeggios are nothing more than broken chords, so they are perfect to use when creating beginning bass lines. for example, the use of 7th chord arpeggios only in a walking bass line reinforces the sound of the chord for the listener, and helps to keep the lines as 'inside' as possible for players who haven't yet refined their ability to spontaneously recognize chord colors.
from there, i add scale tones to the mix, which adds to the number of possible notes that can be played under each chord. subsequently, the number of tones to choose from changes from 4 (number of unique chord tones in a 7th chord) to 7 (the number of scale degrees in any modal scale or similar). the use of scale tones essentially 'shortens' the distance between the notes chosen from, so that the resulting bass lines start to sound more cohesive and linear...
traditional jazz walking lines incorporate a heavy use of chromaticisms. this is what contributes to their connectivity and melodicism. once you have the chord tone and scale tone approach well in hand, you can add chromaticisms to the mix to create even more tightly-connected phrases in your walking lines.
one way to get started quickly creating somewhat traditional sounding lines is to practice what some have referred to as the 'poor man's' approach to building jazz walking lines... this is essentially a hybrid approach that combines tier 2 and 3, as mentioned before...
the hybrid method would work like this: assuming you are working in 4/4 time, playing 4 quarter notes per measure, you would follow this format for each beat within each measure:
beat 1 -> play the root of the chord
beat 2 -> play a scale tone that is compatible with the chord
beat 3 -> play a scale tone that is compatible with the chord
beat 4 -> play a chromaticism that is either a half step above or below the root of the next chord (beat 1 of the following measure)
although this reads as a quick and dirty solution, the resulting lines actually end up sounding surprisingly legitimate. so if you've never tried this before, give it a shot and see how it goes! | 
