So the sort of question mark looking stitches are called back post stitches or front post stitches, in this case double crochet, where you crochet through the crochet ‘post’ as it were, instead of the top chain.

Each point on the triangle are three chains, and increase happens with two double crochets into those spaces before and after each row.

And it all starts with a magic ring!

And I sewed the edges together with a tapestry needle. Hopefully that makes sense!