“Google Social Search is a feature designed to help you discover relevant publicly-accessible content from your social circle, a set of online friends and contacts. The idea is that content from your friends and social contacts is often more relevant to you than content from strangers. For example, a movie review from an expert is useful, but a movie review from your best friend can be even better.”
This YouTube video explains the search tool very well.
I find Google Social Search to be very helpful with my work. For example, I did a social search on Airliners and had a list of resources from people across the world, in my social circle, working in my same field of work. The results were relevant, timely, and extensive.
First you will need a Google Profile. If you already have a Google account of some flavor (gmail, calendar, docs, etc.) log into that account, then navigate to Google Profile and create your profile. Google social search uses links on your Google Profile (Twitter, WordPress, Moodle, Delicious), and people in your Google Contacts to create your social circle.
Next, to conduct a social search, navigate to Google Web Search and enter your search terms.
Click the Show options link at the top of the search results.
It was quite interesting to view my Social Circle. My contacts are listed alphabetically with how I am connected to them (Twitter, blog, Google Reader, Delicious, Wikispaces, Flickr, Youtube, chat, etc). The secondary connections in my social circle that develop from my direct connections are surprising (Astronomy Magazine, Bangkok Post, Daniel Pink, etc).