Hi,
Sanbox is fully featured Testing environment for paypal IPG.In other words its mirror for the original paypal. You have to create a account first here.
https://developer.paypal.com/
And this will describe the process.
https://www.paypal.com/IntegrationCe...c_sandbox.html
My Suggestion to all newbies to paypal,
PLEASE read the INSTUCTIONS before you start.(user manuals as Atli given)
Because what you need is almost available at paypal side, only thing you should know, you have to learn how to use them.
Come back any time for any issue.
Thanks!
-Ajaxrand