Ok, so we're going to be talking about chords and notes here...
First off, chords are made up of two or more notes, typically notes that sound good together. Your double bass has strings that are tuned to E, A, D and G. As you stop those strings with your fingers, you make their sound go higher. You've been doing this in classical music all the time, and you've undoubtedly also learned to read music enough to know where the individual notes are on the double bass when you stop them.
The Nashville Numbering System (aka NNS or "Nashville") is an alternative way to convey how songs generally go in writing or in hand signals. It specifically deals with chords, but also can imply the notes that those chords are made of.
The numbers in Nashville correspond to specific notes which imply the chords those notes stand for. For example, the chord names, ignoring flats or sharps, are:
Key of A -- (1) A, (2) B, (3) C, (4) D, (5) E, (6) F, (7) G
Key of C -- (1) C, (2) D, (3) E, (4) F, (5) G, (6) A, (7) B
Key of D -- (1) D, (2) E, (3) F, (4) G, (5) A, (6) B, (7) C
Key of G -- (1) G, (2) A, (3) B, (4) C, (5) D, (6) E, (7) F
etc...
Usually with "Nashville", the 1, 4 and 5 chords for very simple bluegrass double bass, you'll just play as 2-note chords, alternating one note at a time on the beat, for as long as those notes are called for. As mentioned, the 1, 4 and 5 chords in the key of G are the G chord, the C chord and the D chord.
For Columbus Stockade Blues, the chords are all simple major chords, and these chords also follow the same pattern, they contain the 1st note, the 4th note and 5th note, making up the major triad... But as mentioned for this song on double bass you can just use the 1st note and the 5th note to make the chord.
-- So for the two-note 1 chord or G chord, on the double bass you'll want to locate and pizz the G note (the open first string), and the D note (the open second string).
-- For the two-note 4 chord or C chord, you'll want to locate the C note (for simplicity I'll just have you stop the first string at the 5th note, or C) and the G note (for simplicity I'll have you stop the second string at the 5th note, or G).
-- For the two-note 5 or D chord, you'll want to locate the D note (The open 2nd string) and the A note (the open 3rd string).
So for example In a 4/4 measure using the 1 chord, you'll play the G and D and G and D notes on the beats, for the 1 or G chord... And so on for complete measures that use the other chords.
It will be extremely rare in bluegrass for you to ever need to intentionally pizz more than one note at a time. I don't think I've ever needed to. So again, we're just talking about one note at a time, on beat.
It's really complicated trying to write this out and it may be very complicated trying to read it, but in application it's pretty simple. I'm sure you already know the notes on your fingerboard, but you probably don't know how to address them together for chords, meaning you may also need some help for fingering notes as chords. You may also want some help with your right hand for pizz.
And note, this does not talk at all about playing by ear, we'll worry about that later. This is just a simple and probably crude start-up of how to follow a Nashville Numbering System chart. And as
@AGCurry has mentioned, this is not tablature. Some people may have put bluegrass tab together for double bass, but Nashville is much more commonly used... So common that it isn't unusual in bluegrass jams to have someone raising fingers indicating the Nashville chord number to play at a certain moment.
Let us know as questions come up. After looking over this modest effort to explain, I'm sure you'll have some. Bring 'em on.
