If you have a US-based account, you can choose to accept payments directly from bank accounts (ACH or e-checks.)
1) Create a payment form
2) Scroll to the Payment Methods section
3) Choose "Yes" for the Bank Account option
4) If you'd like to accept both credit/debit card payments and ACH payments on your payment form, you can re-order which payment option appears first to the payer at checkout.
5) Now, at the payment section on your payment form at checkout, your payers will see the option to pay with their bank account.