who's yuko actually?
you guys have idea about yuko?
the connection between her and clow?
and why yuko always demand for price?
btw, my english not very good
hopeyou can understand
To understand who Yuko is a bit better you need to read TRC's sister manga, xxxHOLiC, which centres on her and Watanuki.
To sum it up, Yuko and Clow Reed knew each other and had a strained-at-best relationship (in xxxHOLiC Yuko calls him all sorts of names - four-eyed demon, evil guy etc), but they were able to work together to create the two Mokonas and the earrings they hold (one a tool for magic and one a tool for sealing). They prepared for several people - first, Sakura and Syaoran Li (in their world - this is implied when Yuko says she knows about them), Kimihiro Watanuki, and then Sakura and Syaoran from Clow Country.
I hope that helps, it's all I can infer for the moment.