vCenter Single Sign On (SSO) is a new feature in vSphere 5.1, as with any new feature people need to know where it fits in the stack, why its there and how its going to make things easier?
VMware have done a great job in giving lots of information on this feature, firstly the overview videos are a great place to start, see how SSO fits into the vCloud Suite and what advantages it offers you and how to easily manage it below, following that there are some great blog posts and documentation links I have added to this post for your reference.
Install vCenter Single Sign On as Part of a vCenter Server Simple Install
Install vCenter Single Sign On as a New Installation
Install vCenter Single Sign On, vCenter Inventory Service, and vCenter Server Separately
SSO Frequently asked questions