Maria, are you asking whether it's possible to share the form to add an isheet record publicly where the public users see only certain fields, similar to a view only showing certain fields?

When you configure an iSheet to be shared that creates this group with access to the sheet:

Then you can use column level permissions to grant or deny this group access to specific columns. Removing this group's access to a column will have the effect of hiding it and mimicking what you would do in a view.

There is another way to achieve this which would make sense if you had multiple versions of the iSheet you wanted to share. For ex, show only Fields A and B to some public users and show Fields A and C to other public users.

Create a different iSheet for each public audience with the fields that each can access and also create a master isheet with all the fields. Then use workflow to trigger the creation of a master sheet record each time a record in one of the other isheets is created, using the newly created record's data.