sensational knitted socks

[shellebelle216]

I am working a sock pattern out of Sensational Knitted socks. This is the first time I have tried one out of this book and I am very new at sock knitting. I am about to divide the sts for the heel flap and I am stcuk on trying to figure out what "Rearrange sts to center patt over instep" is trying to tell me to do. And why do I have to unknit last purl st of rnd?

Thanks for any help!