Google drive= your cloud storage (so if you had stuff previously it will.still be there)
Google+= googles answer to Facebook(kind of) and your one stop shop for logging I to stuff.
Google docs, sheet etc= your office suite and you can work offline.
Photos=your photo storage, if you have google+ you get more photo storage. If you have an android phone get it to automatically back your photos up to google photos.
To access your hard drive you click on the files app.
Airdroid fire up the app when you are connected to your WiFi. Type in the address your.phone gives you in chrome AMD boom you’re in. Sign in with your google+ account (no new sign up needed) and go crazy transferring stuff.
I am a Chromebook convert.