Modifying user settings isn't something I do everyday but it is necessary occasionally
You can add a user with the useradd command
usermod is useful for working on a current users priveleges.
The most common use I have for it is adding my user to a group for additional priveleges
make sure to use the -a or you will remove them from other groups
usermod -a -G groupname username
For example we want to add Ted to the foo group
usermod -a -G foo Ted
You can see all the available usergroups in your /etc/group fiile
Other usermod functions:
1 Change a users primary group
usermod -g groupname username
2. Set an expiration date for a user account
usermod -e YYYY-MM-DD username
this is useful if you want a friend to have temporary access to your machine
3. Change users home directory
usermod -d filepath username
4. change users login name
usermod -l newusername currentusername
5. Lock a user account to prevent them from logging in
usermod -L username
To unlock them
usermod -U username
6. change user shell
usermod -s shell path username
for example
usermod -s /bin/bash Ted
will set teds shell to bash
Associated command to usermod
id username
will give you info on the user such as uuid groups etc.