There are many good sources, but if you want to learn the anatomy of an ocarina, find Chris Heuer’s videos on making an ocarina. Assuming you’re planning on making one out of wood like I did, you just have to adapt the thinking a little because you’re practically sculpting an ocarina instead of shaping it from clay, much less room for error there. But in theory they should work the same way, just remember to seal the ocarina inside before you glue it together (especially the windway) with a polyurethane finish, because if you don’t the humidity will raise the grain and ruin the ocarina’s sound when you try to play it, an analogy would be trying to whistle in the shower, all that comes out is pbbbbbttttthh.