Help please tell me how this happen

My galaxy gear to watch I synced it with the Bluetooth device then I turned on my headphones that are Bluetooth also I can hear music out of my headphones as well as use my watch how is it both are connected if they are both bluetooth
I know i am asking a stupid question however I am sorry I do know the answer as yet. Can you please tell me what is the actual meaning of backing up the data which is on a smart phone (I mean android). As far as I understand it means storing whatever the data you have on your phone on an external data storage device. Or does it mean you can back it on things like Google Drive or DropBox or OneDrive etc etc and then you can restore it when you need. But is it safe? I know if I am questioning the security of saving the data on these things then I should stop using emails as well. But I use Gmail which is from Google who is globally acknowledged and widely known likewise email service from Microsoft ( Although I am not a billionaire yet there are a few things which I have saved digitally that I cannot afford to be leaked and misused. What is the simplest and safest way to back my phone data? My phone model is Samsung Galaxy Note 3 Neo. In my opinion it is saving it on a memory card externally and as such. However I am not sure whether it will save things the way they were; when they were on my phone like my contact numbers, word docs, excel files. Can I save all my phone data externally on a memory card?