Payment options for giving can be different for each organization you give towards.
You can give by debit or credit card to all organizations. However, some may restrict the type of card brands accepted to exclude Amex or Discover. Card brands accepted by your organization will appear under the card number blank when on the payment method page.
ACH is the option to give directly from your bank account by entering your account & routing number instead of using a card. Some choose to accept ACH, others do not.
If you have a card or bank account saved to your profile and it isn't a visible choice when trying to give to your organization, that means that the organization does not accept that type of payment.