To set up authorize.net, as a sandbox mode (test account mode) you can:
Note the "login id", and "transaction key" from this account.
2) Login to your emailmeform.com account, and create a form with payment enabled fields (such as "Price", "Drop-down menu", "Multiple-Choice" etc.).
3) In the Form Manager, mouse over this form you just created and want to apply authorize.net to, and click "Options", then "Payment".
4) In the first tab, "Merchant Setup", enter the authorize.net information from step 1. Select "Sandbox Mode" to run a test transaction.
5) Enter your "Payment Options" in the next tab. This is all up to your preference. If you have no preference, the default values should be ok.
Note: if you would like to be notified regarding payment statuses, you must select from the drop-down menu "Notify payment status when", and select "every payment".
6) Next, go to the "Assign Prices" tab and apply prices to the payment enabled fields you set up in step 2. Click "Enable Payment", and then "Save".
7) Click the EmailMeForm logo on the top navigation, this will take you back to the Form Manager. Click "Options" on your form, then "Preview" to view your form, and run a test transaction (you are in sandbox mode still).
8) If the transaction is successful in Sandbox Mode, you can go to authorize.net and set up a real account, then replace the test information in the Payment module (Step 4, Merchant Setup) on emailmeform.com (in your account), and then finally click off of Sandbox Mode and send that link for your form to your users.