Invoices for an account can be created automatically or manually.
This setting, as well as more options, can be set general in the financial tab of the settings section.
These settings are copied into a new account on account creation.
In the account settings, you can divert from these copied invoice settings. These settings can be found in the financial tab of the account settings pop-up.
If you choose to invoice manually, you can do this from the account screen, or for more or all accounts...