How can I have my invoices send out automatically?

You can create a billing schedule where the customers can be billing from a sales order automatically and check the preference to send the Invoice as email automatically.

We use Advanced Billing to establish billing schedules which allow you to specify a number a variables for billing purposes. For example, we offer a number of depot service contracts with flexible terms and payment options. We may have a customer that wants an annual contract, billed monthly. We create a Billing Schedule to split the total amount over a period of 12 months and invoice 1/12 on the same date of each month. The advanced rev rec keeps our revenue in line throughout the periods to ensure proper accounting. We have billing schedules created to accommodate monthly, quarterly, semi-annual and annual installment options for terms ranging from a single month to 5 years. The sales order transaction maintains a status of "Pending Billing" through the duration of the billing schedule where each time a bill date arrives, NetSuite automatically creates the monthly invoice and our Email Invoice workflow picks them all up through a day-end process and emails to the customer each night. Completely hands off process ensuring we never miss a scheduled invoice creation or delivery! Hope this helps!

If you mean how to send out the created invoices as PDF, I would suggest to use a scheduled workflow