The brackets [ ] indicate your input. Do not include the brackets in the command.
useradd -g users -G disk,cdrom,plugdev,wheel,lp -d /home/[user name]/ -s /bin/bash -m [user name]
This will add your user name plus add the user to the following groups: disk,cdrom,plugdev,wheel,sys,lp. Each group gives or denies the user permission to a specific part of the operating system or device. To see all the groups try: less /etc/group
disk - gives the user access to disk drives.
cdrom - same
plugdev- I beleive plug-dev are usb devices.
wheel - you may not want to add for security reasons.
lp - enables access to hp-toolbox for printers and scanners.
The, -d /home/[user name]/, creates a personal directory for your user in the /home/ directory.
-s /bin/bash enables you to use the bash command line as default. Google bash linux
hope this helps