Auto-Close is the process to charge and close any open invoice. Any invoice created and not paid off will appear on the "Open Invoice" list under the "Reports" tab.
An explanation of Invoices can be found here:
Invoices can be closed different ways, and also depends on the day you want them to "Auto Close". Auto closing will charge the account that the invoice is attached to.
There's a couple of ways to approach this. One way is set to the 1st of the month and is automatic. The other way is manually on any date you chose.
Auto Close at the 1st of the Month
Go to Settings tab. Go to Settings. Head to "Financial Settings". You will see an option to "auto close invoices at the first of the month". This will automatically close any invoice that is open, every 1st of the month.
Auto Close Manually
*This process will close the invoices on the day you run the process.
If you leave that option to off, then you can batch close your invoices manually. Go to Reports > Open Invoices.
Click on the top toggle to select all.
Then batch select all invoices and hit "set to auto charge" (found at the bottom of the list)