Once I have Embroidery Threads (or other treads), what do I do with them?
Also, same question for Anuran's racial crafting.
Please answer

you need to then learn an specific potion or item to be crafted skill which is level dependent. Then you will need to use the thread or muddy potion as one of the ingredient in making the next item/potion. see http://wiki.aeriagames.com/edeneternal/index.php?title=Alchemy for anuran potion.

Lestat gives a quick run down of the halfkin crafting here.

Loch_yeti wrote:

Lestat gives a quick run down of the halfkin crafting here.

Yes, it tells how to make threads. But once I have them, what do I do with them?

lestat_anil wrote:

4. Once the experience bar is full, clicking the "learn" button will cause an enchantment corresponding to the level of the thread to appear in the production window. The higher the level of the thread, the higher the minimum level of trophy the enchantment can be used on.

Basically keep making those threads untill you have full exp in that thread. Then you can learn one of the possible enchants for that level. Once you have an enchantment to make you select it and it will show at the bottom of the screen what items you need to make it.

I haven't done halfkin crafting myself but it should be very similar to the frogs crafting.

yep. you need to fully master the thread/muddy potion making skill and then you'll gain access to train a racial skill that uses the thread/potion you've made.