The +1 button is shorthand for "this is pretty cool" or "you should check this out."
To recommend something, all you have to do is click +1 on a webpage or ad you find useful. These +1's will then start appearing in Google's search results," explains Google.
Click +1 to publicly give something your stamp of approval. Your +1's can help friends, contacts, and others on the web find the best stuff when they search.
Currently available for English searches on Google.com.