PayPal is an available COOLSite payment processor for your website.

PayPal Payments Standard
Credentials are set in the COOLSite Admin under Configuration > Payment Processor > Manual.
This method requires your customers to have their own PayPal account.
Customers do not enter credit card info on your website since it's already within the customers PayPal account.
PayPal Standard is considered a "Manual" payment processor within COOLSite because the funds transfer directly through PayPal's website.  This means the COOLSite orders will always be marked as payment pending so you can manually login to your PayPal account to verify the funds transferred.  In Summary its a transaction from PayPal account 1 to PayPal account 2.  The shopping cart Total amount and the customers PayPal email address are passed over to your PayPal Standard account all directly through PayPal's website.

PayPal Payments Advanced & Pro
Credentials are in the COOLSite Admin under Configuration > Payment Processor > Real Time.
Allows you to accept credit cards directly on your website so the whole process stays branded under your company.
PayPal Pro is a "Real Time" payment processor within COOLSite because the funds are securely passed in real time through the PayPal Pro Gateway to your merchant bank and PayPal gives the order a response if the funds/payment was accepted.  This way you would immediately receive an email about the COOLSite Order that would say Payment Accepted or Payment Declined so you do not have to login to your merchant bank every time an order takes place.

Comparison Between Standard, Advanced and Pro

Obtaining PayPal Advanced & Pro API Credentials:

1)  Log into PayPal and click My Account - Profile.
2)  Click API Access.
3)  Click Request API Credentials.
4)  Check Request API signature and click Agree and Submit.
5)  The View API Signature page displays your API credentials.
6)  To complete the process, click Done.
7)  From the Setting up PayPal API Credentials and Permissions page, click Grant API Permission in the left-hand box.
8)  On the Give Third-Party API Permissions page.
        a. Fill Enter API account username textbox with API username that you requested before.
        b  Set checkboxes Direct payment and Express checkout
        c. Click Submit button
9)  On the Confirm API Permission page click Give Permission button.
10) You have finished PayPal configuration.
11) Finally Enter the Pay Pal API username, API password and API signature in your COOLSite Admin under Configuration - Payment Processor - Real Time.

Updated PayPal related steps can be found directly on PayPal's website under: > Integration Center > How to > Website Payments Pro > API Basics.

PayPal API Error Codes can be checked at:
PayPal API Developer Home > How to > API > API Reference > API Error Codes.