Add Paypal checkout for Spree

The RailsEnvy guys begin their own casts business---Envycast .They used the Spree to build the site, and allow customer checkout by Paypal.
Some days ago, I use Spree in a site.I think it's better than substruct,because it's more simple and extendable. I also needed to integrate Paypal to it, but some thing make me confused.
1) There are many ways to integrate Paypal, and many articles introduced these ways.First you need to know which way would you like to use? I used Website Payments Standard , if you don't use this way, this article maybe not help you.

2) For test it, you need signup a develop account,then use this account to create a buyer account, and a seller account.

3) When you test your application, you must login the develop account.

4) install the Spree Paypal extension , this extension isn't mature, but can be used.

5) change the extension's default account and some urls to your own

5)there are some html field the paypal server can accept, you need to find what you would like to use.