From a corporate perspective SAP FSN represents a cloud extension to SAP ERP, of course there is far more in SAP FSN than that. I already created a blog introducing it in a more generic way (daniel.bianchin/blog/2013/10/03/evolving-financial-services-to-another-level--sap-fsn-eurofinance-2013) and added references to other documents.
For those of you who want to have all the details on the basic out-of-the-box outgoing payment & statement scenario, you can find in my document "How-to connecto to SAP FSN"
Feedback and questions are always welcome!
Daniel