Heres an example that should help:
Lets take the simple C Chord on which you play the root or C note (3rd fret, A String). The all important lower 5th or G note is right next to the C on the E String while the upper 5th is only 2 frets up on the D String. The octave C is right next to that on the G String.
This is true for all chords up the fretboard. The upper 5th is 2 up, one string over, the octave is 2 up, two strings over, and the lower 5th is same fret one string lower.
To see how it looks go here:
Bass Guitar Chords
Cheers!