It's pretty easy...
1. Login
2. Click the "Merchant Services" on the main menu.
3. Create your "Buy Now" button by clicking here:
https://www.paypal.com/id/cgi-bin/webscr?cmd=_web-tools
4. Click the "Create Button" below the page when you're done.
5. Choose "
Email" instead of "Website" when viewing your HTML code.
That is your paypal payment link.
Hope that helps!