Take the puzzle-like pieces made of polystyrene and fit all the pieces together according to the picture on the instructions which are included in the box.
You can glue the parts together using a low temperature "Cool Melt" glue gun. Take care that glue is not too hot as it could melt the polystyrene.
Next glue the bottom polystyrene plate which serves as the base of the decoration frame.
Once that is done glue the corrugated cardboard to the edge of the back wall.
Begin at the base of decorations frame.
Glue the cardboard in such way that smooth/flat side is facing outside and corrugated side is facing inside.
Glue only short lengths of cardboard at time, make sure that the glue has fully cooled/dried and then continue to glue the next short length of cardboard.
Continue this way until you have glued the cardboard side wall to the whole edge of the back wall.
The cardboard roll fits 100% of all the shapes, so this procedure is quite simple.
Once you get to the other side of the base remove the excess length of cardboard using scissors and glue the remaining length of cardboard to the edge of the back wall.
Once the decoration frame is completely assembled it can be filled with balloons of different sizes and colours. Balloons can be attached into the frame using Balloon Sticky Dots, double-sided adhesive tape or a low temperature glue gun.