Truebill supports various types of accounts. To link an account to Truebill in the app head to the Dashboard and tap the "Manage" button. From there, tap the "+ Add Account" link and search for your bank. When you're asked for credentials it's asking for your online banking credentials.
If your bank or financial institution is not on the list try searching by another name. If it does not appear in the search, it means that Truebill does not support that institution at this time.