To craft items in Shadow Lords you need to earn crafting materials from doing fights in Shadow Lords. When you first start you will not have many materials so you will not end up crafting much.
As time goes on and you play through several games you will earn quite a bit of materials and be able to make a lot of items very quickly.
To earn this quickly you can check the Emporium after each day and craft what you have the materials to craft, but I personally recommend just letting it come with time.
I would check the Emporium every time it said there were new items and I would make sure I had one of each item crafted. Once I had one of each item I would craft two of each item, then three. Currently in my Shadow Lords I have at least 10 of each item crafted so 250 items sounds like a lot, but you will end up doing it without even realizing it.