Creating a report requires that you already have a Report Template that specifies the configuration of the report for the report type you are trying to run. You will use that Report Template ID when creating reports.
You can find your report template IDs in Dashboard > Reports > Templates.
Different report types require different attributes within the input. Parameters are passed in as a JSON-encoded object in the request body, as described here: Serialization
You can find list of supported report types and examples here: Supported Report Types and Examples