If I'm right, that model runs Android's Marshmallow flavour so you would need to declare the storage either Internal or Portable storage in Settings>More>Storage.
Before you can Root you need to go into Settings>More>About Device and tap Build Number seven times. You are then a Developer and your first task is to enable USB Debugging.
That done, you can download KingoRoot on to your PC and connect the phone with a USB/Micro USB cable. Run KingoRoot and you're done but it doesn't need to be rooted to carry out that Storage allocation function.
EDIT: It should be made clear that manufacturers and retailers of mobile 'phones frequently mess with basic Android systems to suit their own reasons so if they don't want you to do something, it could be why that something doesn't work.
I just looked up the Pixi and it seems to be very basic machine so my suspicion is it's been tweaked.