Here is a little example from the script I use for creating my posts.

TITLE=$(whiptail --inputbox "Enter the post's title:" 10 60 3>&1 1>&2 2>&3)

There are many more dialog types that can be used:

• msgbox
• yesno
• infobox
• inputbox
• passwordbox
• textbox
• menu
• checklist
• radiolist
• gauge

The last one here is gauge which can be tricky to get working, thankfully there is a good StackOverflow post here, which suggests this code:

for i in {1..100}; do
   sleep 0.1
   export TERM=linux
   echo $i | whiptail --gauge "Doing something" 10 50 $i
done