How can we add custom fields (apart from the fields provided) and where can we access the data that we received from these custom fields ?
We would like to inform you that for adding custom fields in user registration form you need to create metafields first. For example if you wish to add a field for company address in user registration form you need to create a metafield first (Please note that metafields are available for Premium Plan and above). You can create a metafield from Admin Panel >> Advanced Settings >> Metafields. Now Click on Add New button. In name section select ms.users and in field enter company_address (metafield name does not accepts upper case letters and spaces you can use underscore "_" instead) and select the type. Now, go to Admin Panel>> Site >> Forms and edit the form named register. Add the custom field and enter the field label, enter metafields.company_address in the name section select the type and save. This field will now be visible in user registration form and the data captured from this fields can be accessed from Admin Panel>> Users.
For further information please refer to the following help center topics: