If you are using removable disk or USB key then you should look at this lesson. I will show you how you can safely remove your device from computer without the fear of losing data.
If you want to receive your Gmail emails, synchronize and backup your contacts, calendars, media or to simply download an app from the Play Store, you need to add your Gmail account on the LG G2.
You just bought Nexus 4 and you don't know anything about Android operating system, so I will guide you through literally first steps on this great phone.