Paypal API Integration into ASP.Net Web Site

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C#

ASP.NET

PayPal

I currently am working on implementing an eCommerce site. I would like to integrate the PayPal API but I am having some trouble figuring out where to start.

I have downloaded the Named Value Pair SDK from this page.

I was able to compile and run the example project by deleting the outdated csproj file and just opening the whole directory as a web site. I have been studying the code and some similar questions in other forums and am starting to understand this a bit but I must admit I'm a bit overwhelmed.

If one wants to integrate the API into a solution, which files need to be included? I see several DLLs and a few Classes which seem necessary, but also a ton of other files. I can't seem to figure out which are "examples" and which ones are required for the API to function correctly.

I need to accomplish the following:
- Checkout by entering credit card info on site (Website Payments Pro)
- Regular PayPal checkout and checkout Express (I have accomplished this through a basic form, but I assume there is a more elegant way to perform this via the API?)
- Notification by PayPal on status of payment so that local order information can be updated.

Sorry if this seems a bit jumbled but I admit I am new to this type of thing.

Thanks in advance.