Every invoice starts from the Create Invoice screen under Pay & Get Paid, where you add a customer's email, line items with quantities and prices, any tax or discount, and a due date. PayPal generates a hosted invoice with its own link, which you can send through PayPal's email or copy and send yourself through whatever channel you'd use anyway.
A customer doesn't need a PayPal account to pay it. They can pay as a guest with a card directly on the invoice page, which is a real difference from a standard checkout button that nudges people toward signing up first. That guest option is a big part of why invoicing gets used for one-off business-to-business payments where the customer isn't a PayPal regular.
You can save an invoice's details as a template and reuse it, which covers most of what people mean by 'paypal invoice template' or 'invoice generator' searches, a faster starting point, not a blank form every time. It doesn't, on its own, send that invoice again automatically on a schedule. Each one still gets created and sent as its own action unless something's built to trigger it.
Paying a PayPal invoice is treated the same as any other commercial payment. The standard transaction fee comes out before the money lands in your account, the same as a regular Goods & Services sale, not a separate invoicing charge billed afterward.