From the plugin's configuration panel, either of the services can be chosen. Click the one you would like to use and press Save Changes.
Using Text Annotation
Visitors to your site can now annotate pages by highlighting text and typing into the corresponding dialog boxes. If users do not have accounts with hypothes.is or annotateit.org, they will be prompted to create one.
Once annotations have been added, pages will display them via highlighted text which can be hovered over (hypothes.is) or clicked (annotateit.org) to reveal the notation.
For more information about how the annotations will appear, and how they function, please see the website for the service which you select.