sudo usermod -aG
sudo usermod -aG <group> <user>
Risk: Careful
What it does
Changes a user, for example adds them to a group.
When to use it
To put someone on a team. Never forget the -a.
Example
$ sudo usermod -aG kitchen ainaAdd Aina to the kitchen team, keeping her other teams.
Learn it in: Users, groups and sudo · Official docs