When you enter multiple By variables, Minitab enables the Show all combinations checkbox. Select this option to create a separate correlogram for each combination of groups created by the By variables. If you do not select this option, Minitab creates a plot for each group of each By variable.
For example, the first By variable has 2 groups, Male and Female, and the second By variable has 2 groups, Employed and Unemployed. If you select Show all combinations, Minitab creates 4 separate plots for the combinations of Male/Employed, Male/Unemployed, Female/Employed, and Female/Unemployed. If you do not select Show all combinations, Minitab creates 4 separate plots for Male, Female, Employed, and Unemployed.