This is a cute idea for a crocheted embellishment. Basically, you crochet a 6-sided granny square, then fold it to make it into a butterfly. To make the granny square, you'll need to know how to single crochet, chain stitch, double crochet, and reverse double crochet.
The only materials you'll need ...
Solomon's Knot stitch (also known as Lover's Knot stitch) is a decorative, lacy crochet stitch that would be ideal for a scarf. This video shows one way to create the Solomon's Knot stitch.
Sewing in your yarn tails when you've finished crocheting can be tedious, but doing it properly makes for a much more polished look in your finished item. Teresa from The Art of Crochet shows how to do this successfully.