I have an example site with special future to integrate my website

this about custom form,

if you check this website https://ckp.ie/ there is a button called  Report Property Issue

when you click it you will redirect a form, so you can choose what issue you facing and when you click an issue it will bring you sub issue

so I need to create this type form using Squarespace 

so how should I do it? really appreciate your help