Google +1 Button for websites is a ranking signal for webpages similarly to Facebook Likes or Tweet. This button lets you endorse pages on a website that you enjoyed reading or recommend on the web. +1 (“Plus One”) is the Google’s social advocacy featured in Google’s search results. These buttons can appear in Google search results, on Google ads and across the web.
All you have to do is click the +1 button, When you see to recommend.
Here’s what Google has to say about +1 button.
The +1 button is shorthand for “this is pretty cool” or “you should check this out.”
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.
Here’s more info on the +1 button.
Adding +1 button to your site
If you are webmaster, here is how to add the +1 button to your site, Just grab a snippet of code from google tool.