So here goes...
Start with apiece of card stock measuring 14.85 cm x 2 1cm, in the uk this is a standard A5 piece of card. Then score along the long side at 7cm and 14cm. Then score diagonally from the top left hand corner to the 7cm score line. Then score from the top the 14cm score line to the bottom right hand side of the card.
This is the basic card blank!
To decorate cut panels as below
Cary ☺ x