Start by opening a photo in your favorite photo app. The gallery app on most devices works well.
In my case the g+ icon is already shown because I use g+ often. If yours is not showm, click the share button.
This will open a menu with all the apps you can share too. The list will have many things like g+, Gmail, other email programs, etc.
One of the great things about Android is this sharing functionality. It is very quick and simple to share content between apps. OK, so now select the app you want to share to. Now all you have to do is click the app to share to. In this case, we want to share to g+ (Google+).
Now just type in any message you want in the text field, select who to share to (this showing I am sharing public but you can select any circles you want). When you are done click the "Share" button on the top right. This will create your new post.
You can share many other things too like complete albums, links, etc.
