How to code curl in C#, .NET

Never, ever, accept code from a insecure website to handle anything to do with real money.
You do not know who is giving you the code, you do not know what it does, you do not know that it places the monies correctly into the appropriate account, without passing the details to any third parties.
And asking total strangers to translate it from one language to another because you don't understand one or the other is just stupidly dangerous.
Only get such code from your payment gateway company - the scope for fraud otherwise is far too large. And remember, you personally could be liable for any monies lost if your action is seen to be negligent - which getting your code from a public forum would most certainly be!
So go back to the provider, and ask for the code in a language you understand, or use the language they provide. That or learn both languages really, really well and translate it yourself...but for your own sake, don't ask total strangers to do it for you!