field 1 CustomerID is autonumber
field 2 RecordID is number
You may be missing something.
In your customer table, you need a unique identifier. So by all means have an autonumber ID field. You might then also have a customer account number (alpha numeric - like S001), and a customer name, which could be unique, but may not be. Company names will be unique, but Individual names won't be. You may have more than one Mr J Smith.
Having an account number as well as the autonumber may be a bit of overkill, but it's still useful.
What you then have is , say, an orders table.
In this table, you have an autonumber field for the record id for the order, and a number field for the customer ID. The value here corresponds to the customers autonumber, but it's not an autonumber in the orders table.
This way, your customer table is related to the orders table, so you can find all the orders for a given customer, or equally, the customer for a given order.
I hope that makes sense.