Group Manager subgroups are used in a situation where you want to keep a permanent subgroup while having the ability to change your main group. Subgroups are created the same way that you would create a normal group. An example would be when you wish to have your staff or helpers have a suffix in chat that marks them like
[Member]Steve[Helper].If the player then ranks up or down but they still retain their suffix like
Create a group:
Add a suffix:
/mangaddv Helper suffix [Helper]
Assign group to player as a subgroup:
/manuaddsub Steve Helper
Now the player Steve will always have a suffix Steve[Helper] no matter what his main group is.