How to create a Donate button by using Paypal:

https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/donate_step_1/

https://developer.paypal.com/webapps/developer/docs/classic/express-checkout/digital-goods/ECDGRecurringPayments/

https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/html_example_donate/

https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/paymentdatatransfer/

https://www.paypal.com/cz/cgi-bin/webscr?cmd=_donate-intro-outside

https://www.paypal.com/us/webapps/mpp/donations