Once you set up your products in E-junkie Seller Admin, we provide ready-made HTML codes for your cart buttons. You would simply copy the codes from us and paste them into the HTML source of your own Web site pages, wherever you want our buttons to appear among your own layout, text and images.
I found this help page for Adobe Muse explaining how to embed HTML codes in your page with Muse:
Our standard cart would appear as an overlay "inside" your own page, fitting within your site's existing layout and branding, or you can use Buy Now buttons that bypass the cart to take buyers directly to instant checkout for just one item at a time. To get the overlay-style cart, be sure to paste at least one copy of your View Cart code into every page with any number of Add to Cart buttons.