How do I get a total to show in document style report?

Create a field to hold this value.

Use an action to calculate the value and save it to that field.

For example, let's say you want a total of all the contracts sold this month.

On the table where your contracts are create a field called “Monthly Total”. When your contract gets marked as sold, have an action that will run a query for all sold contracts marked sold during and including this month. In the expression builder, use the SUM function to get a total of the sold price for all the related contracts.

In your report, you can reference this field. You can't do this calculation directly in the report because the report would repeat for each record found during the query.