单击按钮后如何将用户重定向到页面并将变量POST到该页面，如何进行服务器端处理？

I've got a product page set up where you click a product (radio button) and click checkout with Paypal. What I'd like at this point is to create the purchase in the database (add the table row with purchase details, minus the Paypal receipt id), then send the user to Paypal to pay. When user returns to the site the receipt id will be added to the purchase.I've got a product page set up where you click