^ This.
As in your diagram Bill, each string on a 4 string bass is represented by the 4 lines. You are right that each number is a fret number for that string. Tabs can sometimes point you right to the top end of the fret board, but as you probably know, notes can be played in different positions, on different strings. The Tab in the score is merely telling you where you can find the required note. You may find later that you perhaps find it easier to play the note in another position, on a different string, as you develop a style.
HTH
Al
Edit to correct spelling.