From LedHed's Wiki
Groups
groupadd
groupadd -g 2001 groupname
-g = GID
Users
useradd
useradd -u 2001 -s /bin/false -d /bin/null -c "Users Real Name" -g group username useradd -m username
-u = UID
-s = Shell
-d = Home Directory
-c = Comment (User's Real Name Typically)
-g = Default Group
Modify Users
usermod
Expire Password
chage -d 0
or
passwd -e username