The WAHM shops are quite a new feature.
There are now two sections. The first is for people who make their own products, anything from handmade nappies, to original artwork. These must contain at least 80% homemade items. The other is for retailers, either a WAHM who sells nappies from their home (not homemade), or a small business. Both sections work in the same way. Many of the shops have their own website already, so are using their space as a directory entry, having just one page with a link to their site.
The service is free for a year, and included in the offer is a banner that appears on thenappysite. See here for more details.
There is a help and support section in the nappysite forum.