These denote how you get paid.
We provide a list but you can add to the list if there is a payment method you use that is not there.
Stripe (Credit and Debit cards) are covered in a separate What is. All payment methods mark the invoice as paid unless you mark as unpaid.
If a customer says they are going to pay you by bank transfer you should mark as unpaid and then mark paid when you receive the funds. This way you will be able to keep track of unpaid invoices.
If you are registered with Stripe and you mark as unpaid your customer can pay from their invoice. This will then move from unpaid to paid automatically.