Question: How To Check If I Have Unlocked Bootloader?

[Multed]

Hi fellas!

I recently ordered Mi5s from Gearbest: http://www.gearbest.com/cell-phones/pp_471491.html

Can someone explain how I check if it got an unlocked bootloader when it arrives?
Also, what exactly is the unlocked bootloader? As I understand it I need the bootloader to be unlocked for being able to root, anything else?

Also, should I install SuperSU or Magisk?
I've had SuperSU earlier but as I understand it Magisk is better?

I want to be as free as possible and to install the MIUI 9 weekly builds.

Thanks in advance!
/Marcus