Once you have downloaded your template and unzipped the file to your hard drive, you'll need to get it working in your HTML editor.
The first thing to do when you've opened up Dreamweaver is to define your site - go to Site>New Site from the top menu of Dreamweaver and give your store template a name and browse to the folder you extracted the template to.
You'll find the package has some sample pages, the store .asp or .php pages and a file called Main.dwt in the Templates folder. To make site-wide changes to the design, adding your company name, changing the menu etc. you'll need to work from this file. Once you've made the changes, save the file and you'll be prompted if you want to update all the files using this template - agree to the prompt and you should be able to see the modifications you've made.
Once you have downloaded your zip file you'll need to double click on it and extract the contents of the download to where you want to work from on your hard drive.
Then open Expression Web and go to File > Open Site and browse to where you unzipped the download to. Global changes to the design can be made through the dwt file. This can be found in the Templates folder. Global elements are typically the header section, menu, news and footer.
The User Manual is available here for the shopping cart software.