I have set up osCommerce store and it seems to be installed properly. I don't know how to configure it to work with PayPal Web Payments Standard. I have the PayPal stuff ready to go(API, business account, etc.), but I don't know how to configure it to work with osCommerce. Once there are items in the cart and user checks out, it should go to paypal site for payments handling and shipping and then back to the store on my domain after the transaction is completed.

The payments module is installed, but I don't know where to get all of the information listed in the payment modules:

Your Private Key
What goes here, and where do I find it?

Your Public Certificate
What goes here, and where do I find it?

PayPals Public Certificate
What goes here, and where do I find it?

Your PayPal Public Certificate ID
What goes here, and where do I find it?

Working Directory
What goes here, and where do I find it?

Is this the only thing I need to fill in to get it to work? Do I even need to fill in all of these? I have scoured the paypal dev sites, lunarforums, but nothing seems to be clear or direct. Can anyone help me out, or know how to set this up? I hope I've been clear.
Thanks.

There are several paypal payment modules on the new install.  (one that is very to use/setup -"paypal" - does have its drawbacks)  For the one you mention, I dont think you need to fill those items in.  Do you have an account with sandbox?  You would need this to test.  There are a lot of discussions regarding paypal at forums.oscommerce.com that you might want to read.