I want a form to be popup upon click of button in UI (a form will be there to enter details and open click on button a new form needs to be displayed)
Discussion posts and replies are publicly visible
OOTB you can use record actions to do that. If you add a few more details, we might be able to help you better.
by clicking on approve button , I need a form to popup to enter details
I can achieve it by confirm dialog box ?
Yeah ... not much details here .....
My approach to display "popups" is, to just hide everything else and just show a card layout with shadows enabled. This allows me to do anything I want.