Click to Register a New Client at top right corner.

Enter all required fields

Go to the Permissions tab which shows each permission and their review status

You have to complete one of them. When Instagram approve your Api, Customers can get their images from Instagram.

There are 2 fileds required and important. They are website url (put your site ) and redirect url. Redirect url needs add your domain + “/pdc/index/instagram” see an image.
And then you get 2 fields: Client ID and Client Secret. Enter them to PDC setting in backend magento site.