I'm so sorry.I tried to apply your solution,but I didn't get your answer.So what I did is
echo "choose one of the groups to add the user in

mktg,ent,trade,mgmt)" grpname
read null
cut -f1 -d":" /etc/group
read grpname
echo "Type a username to add: " usrname
read usrname
clear
useradd -d -g $grpname -m -k /etc/skel -s $usrname * I DON'T THINK THIS LINE IS CORRECT
echo "user" $usrname "has been added to " $grpname "group on your machine"
##Display the records for the new users ONLY from /etc/passwd I DON'T KNOW HOW TO DO THIS PART
so that was my work.Thanks for the answer aigles
Belinda