How to read user input into a variable in Bash?

Try this

#/bin/bash

read -p "Enter a word: " word
echo "You entered $word"

Yep, you'll want to do something like this:

echo -n "Enter Fullname: " 
read fullname

Another option would be to have them supply this information on the command line. Getopts is your best bet there.

Using getopts in bash shell script to get long and short command line options

Also you can try zenity !

user=$(zenity --entry --text 'Please enter the username:') || exit 1

Use read -p:

# fullname="USER INPUT"
read -p "Enter fullname: " fullname
# user="USER INPUT"
read -p "Enter user: " user

If you like to get the user's confirmation:

read -p "Continue? (Y/N): " confirm && [[ $confirm == [yY] || $confirm == [yY][eE][sS] ]] || exit 1

You should also quote your variables to prevent pathname expansion and word splitting with spaces:

# passwd "$user"
# mkdir "$home"
# chown "$user:$group" "$home"