In order to load the BURST Floss into the case you must first remove the cover over where the bobbin sits.
This is done by opening the floss case and then turning the case over and pinching and pressing the 2 tabs at the same time.
Turn the case back over and you will be able to lift the cover.
Once this is out you can place the bobbin on the spool and thread the floss to the left and replace the cover, This sits on and clips into place.
Ready, Set ... Floss!
Here is a video on how to do this if you prefer.