Paypal Integration

What he said. You can sign up for a developer account at https://developer.paypal.com/ - this allows you to set up multiple buyer/seller accounts. Keep in mind that Sandbox is fully separated from the live environment; so any emails will be directed to the 'Test emails' section on https://developer.paypal.com/ rather than being sent out externally. Should you need to get specific access to an API call (i.e., Reference Transactions), just log a thread at x.com or paypal.com/mts

For sandbox account, you can go to www.developer.paypal.com and start an account. The basics of paypal integration? Thats too generic to answer but i suggest you go to www.x.com to read up on forum threads.