Third position is found with your first finger over the eighth fret. Like second position, you can't go from A♭ to A♭ here.
Start with a low C, D♭ and E♭ with your first, second and fourth fingers on the fourth string. On the third string, play F, G and A♭ with your first, third and fourth fingers. The G can be played as an open string as well.
You can keep going up with B♭, C and D♭ on the second string with your first, third and fourth fingers, followed by E♭ and F on the first string with your first and third fingers.