The Google photos app will show content that's on your phone as well as what's been uploaded so it is possible to see things that haven;t been sync'd yet. It's worth going into the app's settings to check what syncs and how it does it. I have it set to wifi only to keep mobile data usage down. You'll also find an option to select the folders to back up and one for whether to include videos or not. If a new folder is created, you should get a notification offering to sync it and you can choose whether or not to at that point. It's handy as you probably don't want content from other apps in your Google photos, for instance, but would want you camera shots.
To get "free" storage (that dooesn't eat into your Google allowance), make sure that you have "high quality" and not "original resolution" selected, too. If you have any original res shots there, there's an option to convert them - I can't remember exactly where it is as it's a while since I had to use it, but it was reasonably obvious when I did.
