examples of sign expansion from normal forms of surreal numbers

Question

I am reading Conway's "On Numbers and Games" and in chapter 3, I'm a little confused. In the part where normal forms and sign expansions are discussed together, the direction is to use relevant sign expansion of $y$ in $\omega^yr_y$. But, I can't quite understand the instructions given. Could someone please give some examples of how the relevant sign expansions are found from ordinary sign expansions? And how sign expansions are deduced from normal forms according to the book? I have searched in the internet, but can't find detailed examples anywhere.