How do I know If my phones Bootloader is locked or not?

[Android Central Question]

I want to flash TWRP & SuperSU to take a backup, but I read that if you flash TWRP with a locked bootloader it would brick my device & wipe my data, now that would just defeat the purpose. How do I determine if my device bootloader is locked or not?

I have enabled developer options, enabled USB Debugging, there is a option in the menu 'OEM Unlock', what does it do? Does it wipe data?

Device Model - Samsung Galaxy-J700F