The idea is to organize user management in ubuntu in a simple way so just by looking at it, you are able to know what to do.
sudo adduser yourname
Change User password
sudo passwd user
sudo deluser yourname
Deleting the user account doen't remove the respective home folder. It's up to you whether or not you wish to delete the folder manually or keep it.
Remember, any user added later on with the same UID/GID as the previous owner will now have access to this folder if you have not taken the necessary precautions.
Move deleted User to archived folder
If you'd like to change that, so you can have an achieved folder for those who you deleted, you can do the following to avoid future conflicts:
sudo chown -R root:root /home/username/
sudo mkdir /home/archived_users/
sudo mv /home/username /home/archived_users/
Temporarily lock or unlock a user account
sudo passwd -l username
sudo passwd -u username
Add or Delete a Group
sudo addgroup groupname
sudo delgroup groupname
Add User to Group
sudo adduser username groupname