To Create a group:
Syntax: sudo groupadd groupname

To add the user to the group:
Syntax: sudo usermod -a -G groupname username

To create the user:
Syntax: sudo useradd username

Reference URL's:

https://linuxize.com/post/how-to-add-user-to-group-in-linux/
https://linuxize.com/post/how-to-create-users-in-linux-using-the-useradd-command/