The AIM Method would mean the user is entering the Checkout detail son your site (Local Checkout).
If you are using local checkout, and you have Data Bridge, when you run the checkout wizard, you can configure to have Universal Email send the cart details in an email and not have to rely on the one sent by authorize.net.
The SIM method means going to the Authorize.net server for checkout, using this method, you will need to rely on the receipt sent by Authorize.net. they do not offer much in the way of customizing that receipt.