Your formula will need to live in a different column to the values you wish to sum.
=SUM(B2:B)This excludes the column name, and sums every value beneath it. It will continue to keep total as you add more rows.

Formulas are a feature of Capacities Pro.
Can I use Capacities like an Outliner?
In Capacities you can easily switch between outlining and writing in paragraphs. Go to the settings, navigate to the “Editor”, to "Toggle style" and select “Bullet” for the way toggles behave, so you can collapse child blocks under their parent blocks. Also select “Show full path above” for the "Default display of nested backlinks". You can read more about Capacities as an Outliner on our website.
How can I create a table of contents in Capacities?
You do not need to create a table of contents manually. If you use headings, an automatic one is created for you and available in the right sidebar!