1. Link to your aStore as a stand-alone store (this is what they were offering previously and is as simple as having a link (like this) to your aStore.
2. Embed your aStore using an inline frame – where it will appear as though the aStore is a part of your site and they can shop without leaving your shop (as in the picture above/left).
3. Integrate your aStore using a frameset – placing the aStore in one frame and your site’s navigation into another – also making it seem like it’s part of your site (below).
Instructions for each method are in the ‘get link’ section of the aStore menu.
It’s nice to see Amazon taking their stores in this direction – it answers a lot of the concerns expressed by publishers when they were announced.