You can check if it's saved by going to mail.google.com, contacts.google.com, calendar.google.com, photos.google.com on your computer. Even your timeline can be found.
The how-to can be found on your phone.
Goto settings an type backup.
Tap on Backup settings and when you're there tap on the question mark in the upper right corner of the screen.
Data from from WhatsApp, Signal and other apps have to be backed up from within the app itself.
