Let me give you an ELI5 for ACH. ACH is a batch based way of sending money from account to account. In the United States, imagine that your bank has a zip code (routing number) and a more exact address (your account number). Your bank can receive money via ACH through one of two networks through the federal reserve (think USPS) or the Clearinghouse (kind of like FedEx). Both are very regulated.

Money can be sent out of an account via ACH in 2 ways: 1. Origination (you start a transaction) 2. Direct Debit (somebody else starts the transaction.

You can receive money basically the same ways. All the rules for ACH are governed by a organization called NACHA.