A G major chord, consisting of the notes G, B and D, can be played in many ways on the bass guitar. In root position, the G is the lowest note. In first inversion, the middle note---the B---is the lowest note, and in second inversion, the top note of the triad---the D---is the lowest note. This article will teach you to play all three positions of the G major chord in the bass guitar's lowest range.
Tune your guitar to E-A-D-G, starting with the bottom, thickest string.
Put your second finger between the third and fourth frets on the E string. This is a G. Put your first finger between the second and third frets on the A string. This is a B. Play these notes with the open, unfingered D string. This is a G major chord in root position.
Put your fourth finger between the seventh and eighth frets on the E string. This is a B. Put your second finger on the D string between the fifth and sixth frets. This is a D. Now lay your first finger flat across the D string as well, so that it presses the string down between the fifth and sixth frets. This is a G. Play these three strings together, and you'll hear a G major chord in first inversion.
Put your first finger on the A string between the fifth and sixth frets, and lay that finger across the D string in the same place. These are your B and D notes. Play these together with the open, unfingered G string for a G major chord in second inversion.