Umm, it's pretty straight forward. Black wire is ground on first cell. Second wire, next to ground is cell one positive. 3rd wire is cell #2 positive. 4th would be cell #3 positive, and so on.

Black lead of volt meter to ground and red lead to each positive in order, will give you voltages of cell #1, cells #1 & #2 combined, and cells #1 & #2 & #3 combined, and so on.

To get the second cell reading just subtract cell #1 voltage from your second reading.

To get third cell reading subtract cell #1 & #2, from it.

EXAMPLE : 4.2, 8.4, 12.6, would be what you read on a fully charged 3 cell pack.

Cell #1 is 4.2
Cell #2 is 8.4 - 4.2 = 4.2
Cell #3 is 12.6 - 8.4 = 4.2