Hello,
Bunting has become really popular - I see it everywhere now. As Nikola says, it's a form of decoration, usually square or triangular pieces of cloth or paper attached evenly along a piece of string. To use it, you put it up - that is to hang it across windows, doors, ceilings, from one lamppost to another, so that it flutters and moves, and makes the place look more jolly and festive.
I hope this helps,
best wishes,
Annie