hmmmmmm....
I read to the bottom of the pag I found telling me how to add the user to a group and found this:
The usermod command has two options for adding users to groups. The "-g" option changes the user's primary group. The "-G" option adds users to secondary groups. With the "-G" option, more than one group can be specified by placing a comma (,) between the group names.
If you do not specify the "-a" (append) option with "-G", the user will be removed from all secondary groups except the groups listed.