you can also take a look here http://www.ibass-school.com/practising_scales
for example , in G major scale
position 1 :you begin with the G note on the 4th string and end with the C note on the 1st string
then , position 2 , begin with A note on the 4th string and end with the D note on the 1st string
when you have well memorized the notes in all position , play a rhythm on a beatbox and try improvisation on G key !