WordPress.org

Installation is pretty standard. Just upload the plugin, activate it and check the settings page of the plugin. Here are the details:

1. Upload plugin-name.php to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Get your Google API key
4. Go to the plugin's setting page and enter your Google+ ID and Google API key
5. Make sure to also maintain the other settings on the page
6. After saving the settings, you may want to click on the mass import so that Google+ activities already available on your profile get imported to your blog.