This is a guide I’m mainly written a personal how-to guide, but I hope it can help others.
|Official manual Page||usermod|
This is a fairly generic Linux-based command so it work across different Ubuntu editions and versions.
To add an existing account called ‘account1’ into the ‘group1’ group:
sudo usermod -a -G group1 account1
|-a||add user to the group, works with ‘-G’|
|-G||add user to that additional group as needed|