Communicating with a Service Provider
Before configuring the IdP to communicate with a service provider be sure you have a basic understanding of how the IdP categorizes and works with service providers.
Communication Basics
In the vast majority of cases enabling communication with a service provider simply requires loading its metadata in to the IdP. This could be accomplished in a couple different ways. First, and easiest, is for the service provider to register with a federation whose metadata is already being loaded by the IdP. In this case all you have to do is wait for the metadata refresh (this occurs once a day by default).
However, if the service provider is unable to register with a federation, or your IdP is not a member of a federation, you may load a new metadata source containing the service providers metadata. In most cases the service provider can provide a URL from which to load the metadata and you should use the file-backed HTTP metadata provider to retrieve it.
You may also have to extend the IdP's attribute-filter.xml such that it contains some filter rules that will release some attributes to the SP.
Advanced Configurations
Some service providers, especially those using something other than the Shibboleth Service Provider software, require special tuning of the messages that are sent to them (e.g. attributes pushed to them during the sign on process, certain messages signed or encrypted). These sorts of configurations may be set by creating per service provider configurations.