Batch invoicing is accessed by going to "Vendors" on the menu bar. You will see an option "Create Batch Invoices". This is the screen you will see when you click on this option:
If batch invoicing is done on a regular basis, you might want to create a billing group. This may take a little while to set up, but once it is configured it will only take a few minutes each time you want to create batch invoices. A great time-saver!