Don't go looking for Google+ History. Right now, it's available only to developers so they can support it with their software. Google will make it available to users later.
In a nutshell, Google+ History will make it possible for third-party apps, sites and services to share information about your online activities with Google+. For example, if you post on Twitter, a copy of your tweet will show up in your Google+ profile.
Google+ History doesn't actually share content from the other sites with your friends. Instead, it places it in a secure, private space on Google+ where you -- and only you -- can see it.
If you would like to share any of these items, you have to explicitly take action to do so.
In my opinion, this is how social sharing should work.
Using Google+ History
Details about Google+ History are hard to come by. But it's pretty clear what Google hopes to accomplish.
Right now, Google+ History exists only in the form of an API, a programming interface that enables software components to interact and connect, and as a preview for developers for testing their software.
Google+ History is functionally similar to Google's Instant Upload feature, which automatically uploads pictures you take with your phone to your Google+ profile without sharing them with anyone but you.
When you create a post, you may choose to include any of the phone pictures that have been uploaded via Instant Upload. Or you can ignore them.
In fact, it's helpful to think about Google+ History as an expansion of Instant Uploads -- it expands the types of content that can be "instantly uploaded" and makes "instant upload" functionality available to companies beyond Google.
The magic feature of both Instant Uploads and Google+ History is the instant and automatic uploading of content that is not shared until the user deliberately shares it.
In other words, it doesn't share content for you -- it locks and loads it for you. The content gets shared only if you take action to share it.
Here's how I think users will experience Google+ history.
As third-party websites, online services and mobile apps increasingly support Google+ History, they'll add Google+ to the list of options for sharing what happens on their services. If you agree and choose to authenticate Google+, everything -- or some things -- you do on that service will show up on your Google+ profile, but only where you can see it and nobody else can.
Let's say you use Foursquare and read your favorite tech publication -- the one you're reading now. And let's also say you authenticate these services with Google+ History.
It's Saturday morning. You go to a Starbucks and check in on Foursquare. Then you use your tablet to read an article like the one you're reading now. You're fascinated by this brilliant Mike Elgan guy, and you want to tell your friends on Google+.
So you fire up Google+ and there already waiting for you are both actions, which Google calls "moments": The check-in and the article.
These are sitting on top of an incredibly long list of past "moments" from the apps you've authenticated to work with Google+ History.
Instead of opening a blank window to write a post, you simply choose "Share" from a drop-down menu on the article "moment."
Google+ History will put a thumbnail photo from the originating site, plus a link to that content and a summary. In other words, it will build the basic Google+ post for you. Then you can write an additional sentence or two and click a button to share it.
Of course, you'll choose not to share the Starbucks check-in from Foursquare because, really, who gives a flying frappuccino that you were at Starbucks?