The purpose of this feature is remind multiple customers that they have pending unpaid invoices.
2. How to create a Process Statement Account entry
Now, wait for the emails to get sent if you've enabled "Enable Auto Email" or click on Send Emails to send them immediately.
3.1 Download consolidated PDF of all customers
On creating an entry, there is a button seen at the top called "Download" which lets you see the consolidated report PDF of all customers. You can use this for reviewing.
On creating an entry, there is a button seen at the top called "Send Emails" which lets you trigger email sending manually to the customers. The emails are queued via a background job, which you can track in the "Email Queue" doctype with the DocType and Document references. You can do this even if "Enable Auto Email" is on.
3.3 Using dynamic values in the Email Subject and Body