The input field at 'Selected group name' shows the name of the currently selected group.
If you modify that field, the group will be renamed.
The input field at 'Modify using ACI/SRT' allows scripted modification of group names:
for the currently selected group, the result (of applying that script to the groups name) will always be displayed behind 'Resulting group name' (if an error occurs, it will show there as well).
if you are satisfied with the result, press 'Apply to selected group' to actually change the groups name.
pressing 'Apply to all listed groups' will perform a batch rename for all listed groups.