OpenSAML user discussion

Hi ,

As part of my work assignments, I have come across an requirement where I 
should use SAML to consume the SAML assertions sent by IDP(identity provider)

My project scenario is:
The End-user logs into the application(IDP)successfully and clicks on a 
link(Service Providers). When the user clicks on SP link, the IDP would send 
the SAML assertion in the String format.

As an Service Provider, my application should retrieve the SAML String and 
process(i.e., validate and verify the signature) it. If the signature and 
assertions are ok, then the user would be redirected to actual requested page.

I am new to SAML and in a confusion, where to start to achieve this.
Please can some one guide me how to start with SAML in the above scenario? 
and any help for clarifying the following would be appreciated.

1. Is there any function available for retrieving and processing the SAML 
string in SAML API?
2. How can I use the API to validate and verifying the SAML signature?
3. Any explanation with sample code fragments would be highly appreciated. 

Many Thanks,
Regards,
Amul