[Capt19]

Hello and good morning everyone. My question is : I have to get a replacement G3, having problems with this one rebooting all by itself, how do I transfer everything, photos/videos, contacts, bookmarks, messages, movies, literally everything from the defective unit to the replacement ? Thanks

[Crashdamage]

If you do:
Settings > Backup & restore > Backup my data
...then you can do:
Settings > Backup & restore > Automatic restore
...and your apps will automatically reinstall and WiFi settings and some other stuff is restored.

Go to:
Settings > Accounts > Google > select account
...and enable sync for contacts, calendar, email etc and they will sync back to the phone. Remember, you must save contacts to your Google account for them to resync to a new device.

Photos, music, documents etc must be saved to a cloud service, restored manually or be saved with a backup app such as Helium or MyBackup Pro. Same for SMS/MMS, they are not saved to your Google account. Helium or MyBackup will save SMS/MMS or there's several specialized apps just for hat purpose in the Play store.

MyBackup Pro does not require a PC. Helium is better in that it may save more settings and other data than MyBackup, but still maybe not *everything* and it does require a PC.
https://play.google.com/store/apps/d...id.MyBackupPro
https://play.google.com/store/apps/d...ikdutta.backup

Anyone with a Google account automatically has 15GB free storage on Google Drive. There several other good cloud storage service such as Dropbox, Copy.com, etc. There are apps for both your phone and desktop for cloud services:
https://www.google.com/drive/?authuser=0#home
https://play.google.com/store/apps/d...pps.docs&hl=en
https://www.dropbox.com/en/
https://play.google.com/store/apps/d....android&hl=en

Google Photos works well for photo backups:
https://play.google.com/store/apps/d...s.photos&hl=en

Dropbox is also very good for photos. The Dropbox client linked above for Android has an auto-backup feature.