If you want to test your item button code, there's two options. The first, have someone you know actually test the code, suggest you sit with them and observe the process. Once competed you can do a refund. True hands on learning.
The together option is to use the Sandbox. This is a tool specifically designed for testing as it is a virtual world. Everything done in the Sandbox stays in the Sandbox. Once you have things working as you intended, you can then go live after making a few changes to your test code.
To learn more, start here:
https://developer.paypal.com/
Make sure you spend some quality time reading the guides before jumping in, else you will be clueless.
