Jitu,
Remit uses a REST implementation of Amazon Flexible Payments Service
(FPS). That service is used for one-time charging, "marketplace"
charging (where you perform a charge on behalf of another party,
recurring fees, and a few others. The service itself generally relies
on the construction of custom URLs to which your client (or 3rd party
recipient) will be sent.
All of the transaction processing is handled by Amazon and all of the
client interface is done using Amazon's site in what they term as, the
"Amazon Pipeline". Depending on the type of charging you would like
to perform, there is a unique pipeline to use. It is the generation
of these custom URLs and the handling of the Amazon response (Instant
Payment Notification and client-return parameters) that this library
will aid you in implementing.
As an example, this would be a "simple" implementation of a
"marketplace" charge (one in which you are charging a client for a
product on behalf of another party):
http://gist.github.com/46941
I left out creating your caller token, but if you need it, I can add
it in.
Hope that helps a little,
Nate