This is something similar to the 'like' button on Facebook. If you see something - an article, a product, a forum, it should work with anything - the idea is that if you want your friends to see that you like it, you click the +1 button. You have a tab that shows your full list of 'likes' and you can choose to display the whole list or not. Your 'likes' are shared with a circle of other users, though you decide which groups to share with. However, if anyone lands on the site, page etc that you recommended, they will be able to see your profile whether you've put them in your circle or not - the circles are for alerting people to pages they may like but haven't yet seen.

You need to have a public Google profile to use the function, though how much information you display on the profile is up to you - it can be just your username.

You can learn more about +1 here.