Building forms isn't a built-in functionality in Prismic, but luckily if your website needs to use forms it's easy to set different services alongside Prismic in the frontend of your application.
You have two options when it comes to using forms with Prismic.
Note: Prismic has no affiliation with any of these services. Some have free tiers and others charge, each with their own advantages and disadvantages.
Some of these work natively with Prisimc's Embed field, and for any that don't you can set up a field for custom HTML embed code as explained in this article:
You can set up fields in Prismic to define the text that appears on the form (such as the field name, placeholders, and default text). But the form's functionality needs to be handled on your end or by a third-party service.
On your front end, you will need to set up the form's input fields with the text pulled from Prismic and write the code to determine what happens on submission of the form.