How do I summon a Shadow person

I know there are plently of ways to summon them but ive tried all of them and nothing seems to work. Could summon tell me a good way to summon them?

Pick up a copy of the Shadownomicon by D.H. Thorne. It’s all about working with the shadows.

I might sound like an ignorant, but what’s a shadow person?

I thought they were just a smug on the lent or something