To install this plugin just drag the openphoto-wordphp folder and the file openphoto-wordpress.php into your wp-content/plugins directory.
You'll need to go to Settings->OpenPhoto and enter the name of your OpenPhoto url. This is something like http://current.openphoto.me.
Clicking Save Changes will take you to your OpenPhoto site. You'll need to login, create an app and grant your blog access to it. Once complete you'll be redirected back to your WordPress site.
Click the media icon like you normally would and then select the OpenPhoto tab. Here you'll be able to filter by tags and select the photo to embed into your post.