A card in two parts - the collar shaped base is easier to make than it looks - and all you need to do is stick your topper card on it and you're away!
It's a cute idea, I've done lots of diamond fold cards in the past and the principle is the same - just remember to flatten your creases as you go along!
For the base, cut a piece of card 10cm x 25cm. Score lengthways at 5cm, then across it at 5cm in from each short edge
Then measure and mark, just at the top and bottom edges, another 5cms in from each vertical score line
You then need to score diagonally from the measured points to the point at which your other score lines cross, a bit like an arrow pointing towards each end!
Then a bit of gentle folding and teasing into shape. Your diagonal lines are VALLEY folds, all perpendicular lines are MOUNTAIN folds. Be careful not to extend the creases beyond the scored lines you've made!
This is what you end up with - burnish the creases with a bone folder or scoring tool and you have your collar base to decorate and attach to whatever shape you want to make the main section on the card out of.
NB I don't use a folded card, just a single sheet, in this case cut to an octagon size, and decorated with nifty Craftwork Cards papers! This is the More than Words collection.