UserAdd
useradd(8) creates a user.
Installation
Linux and BSD distributions will either have useradd(8) pre-installed, or direct users to instead use adduser(8).
Usage
useradd USERNAME
There are different opinions regarding how explicit to be with user groups (i.e. the group named the same as a user with the user as the only member). Above, the group is created implicitly. Sometimes the user group is created first with groupadd(8) and set as an option.
groupadd example useradd --gid example example
This is more useful when forcing a specific ID.
groupadd --gid 1234 example useradd --uid 1234 --gid example example
UserMod
To modify an exising user, such as adding them to a new secondary group, use usermod(8).
usermod --append --groups wheel example
UserDel
To delete a user (along with all of their files), use userdel(8).
userdel --remove --selinux-user USERNAME