How to send form submitted data to paypal in Drupal?
I'm the maintainer of Drupal Commerce and of the Commerce PayPal module. I'm afraid your question is too broad to be answerable here, but for folks looking to solve the same issue, you should check out the code in my Commerce PayPal module. It provides a full integration of WPS, WPP, EC, and PPA / Payflow Link.

For general Drupal support, there are much better channels to pursue. I'd look into videos or books specifically focusing on the Forms API or just dive into module code like mine to learn through investigating working examples.