The form is conveniently pre-populated with registered namespaces and a skeleton SPARQL update.
To add a new property to the current resource, simply move to the bottom of the form and type in the SPARQL, then click the Update button.
Example: Add a dc:title property to the current resource:
Example: Delete the inserted dc:title "My Title":
Update the inserted dc:title "My Title" to "My Test Title":