Hi Vasu,
Please do the following at Siteminder end to configure as IDP.
1. create a local entity
2. export the metadata of local entity which is created in step#1
3. when you click on Export metadata, it will ask you to enter the Partnership name, Partnership will be created automatically once you enter the partnership name and the metadata will be exported.
4. You can use this metadata and import at Shibboleth end.
5. Also you would need to get the metadata of Shibboleth (remoteSP) and import at Siteminder.
6. Once you get the remoteSP, you can modify the partnership accordingly and activate it.
And for Shibboleth configuration, Please refer below link.
NativeSPGettingStarted - Shibboleth 2 - Shibboleth Wiki
Thanks,
Sharan