Update README to add clarity to installation and config tips

README.md

@@ -11,6 +11,65 @@ Currently no core files are changed, so you can just upload the files in `/inclu
 
 **Note: You should not copy the README.md, LICENSE or changelog.txt files to your live server.**
 
+
 ### Admin module configuration
-When installing the payment module from your admin > modules > payment, copy the Page ID, Transaction Key, and Response Key from your GGe4 Payment Page "security" settings tab.
+In your store's Admin->Modules->Payment screen, enter the Page ID, Transaction Key, and Response Key from your GGe4 Payment Page "security" settings tab. See the Security section below for help on where to locate this information.
+
+
+## Hosted Checkout Pages Configuration
+
+1. Log into your First Data GGe4 account
+2. Choose Payment Pages
+3. Click on the desired Page ID
+
+There are 9 pages of settings available. The following are the ones that you need to pay attention to:
+
+`1`. General 
+ - Page Title - Whatever you want this page to be named. This will be the title shown on the payment page.
+ - "Return to your Store" URL - the URL to your store.
+ - Enable Level 3 Processing if you want lower rates. Check with your account rep to see if you qualify.
+
+`4`. Receipt Page
+ - Return Link Method: This setting is auto-determined by the HCO module. But if you want to make a choice, choose **REDI** or **AUTO-POST** or **LINK**
+ - "Receipt Link URL" **needs to point to your store's checkout_process page**, which is at:
+
+     `https://your_domain.com/index.php?main_page=checkout_process`
+
+`8`. Appearance
+ - Header Logo: Upload a Logo if you wish to brand your payment page 
+
+`9`. Security 
+ - You will need to enter these settings into your First Data HCO module configuration settings in your Zen Cart Admin:
+  - Payment Page ID
+  - Transaction Key
+  - Response Key
+
+Finally, click `Save Changes` to save all the settings you've altered.
+
+
+### Level 3 Processing Support
+Level 3 support can help reduce your interchange rates/fees.
+
+Zen Cart already passes all the Level 3 data, but if you want to benefit from it, you need to have your account rep enable Level 2 and Level 3 data support in your HCO Terminal. Contact them for assistance.
+
+
+
+## Testing
+
+Testing can be done with a "real" account, if you simply set your module to Testing mode in your Zen Cart Admin. This will let you do test purchases without actually charging a real credit card.  
+
+This is enough for most peoples' use. 
+
+TEST CREDIT CARD NUMBERS: https://support.payeezy.com/hc/en-us/articles/204504235-Using-test-credit-card-numbers
+
+When ready to "go live", simply set the module to "Production" instead of "Testing" in your Zen Cart Admin.
+
+
+## Sandbox for Developers Only
+If you are a developer and will be doing extensive testing of transactions in a store that's not "real", you may wish to create a Sandbox account for this purpose. The sandbox account is a completely different set of credentials, and completely different Hosted Pages than what your "real" account uses. 
+
+To obtain a Developers Sandbox account, request one via https://provisioning.demo.globalgatewaye4.firstdata.com/signup/ ... again, this is for Developer purposes only.
+
+Then use the Security Keys from the Sandbox account when configuring the payment module in your Zen Cart Admin. Also choose Sandbox mode in the module settings so that it knows to send transactions to a special server. 
 
+If you mix up sandbox vs "real" credentials, you will get security errors when attempting to perform transactions.