What is Secure Store Service?
As name implies, it is a store that secures credentials and the service aids mapping to external resources like BCS, Excel Services, Performance Point etc.. and associates those credentials to a specific identity or group of identities. Secure Store Service can be configured in a way that multiple users can access an external system by using a single set of credentials on that external system. (Does it sound similar to Single Sign On from SharePoint 2007?)
For eg., if a user named Harry has one account on the server that is running SharePoint Server and another in a CRM application, the Secure Store mechanism enables his CRM credentials to be stored with his user profile in SharePoint Server. As a result, if he uses a Microsoft Business Connectivity Services (BCS) solution in SharePoint Server to obtain data from the CRM application, SharePoint Server looks up the Secure Store Service database on the server and provides his credentials to CRM. In in this manner, Fred automatically logs on to the CRM application without having to log onto the CRM application separately.
How to check on the service?
Open Central Admin and click on “Manage Service Applications”.
Make sure the status of Secure Store Service is started.
The enabling of this service is the first step that is required to do before connecting SharePoint with any other external Systems.