Nearly all the HTML pages for your online store are kept within a sub-folder on your website called 'acatalog'. The exception to this is the 'Brochure Home Page', which can be uploaded to the directory level above 'acatalog' on your website. See Creating A Brochure Page for more details on the brochure home page.
If you do not want to use a brochure home page, and you just want customers to go straight into the 'acatalog' folder when they first visit your website, then you could do the following:
Copy the following code into 'Notepad' or an equivalent text editor and then save it as 'index.html' somewhere on your PC.
Then, use a standard FTP package to upload the file to the 'document root' of your website. This will usually be the directory that the 'acatalog' folder is within.
<html>
<head>
<meta http-equiv="refresh" content="0; url='http://<mysite>/acatalog'">
<title>Online Store</title>
</head>
<body>
<p>Please wait to be forwarded to our store or press
<a href="http://<mysite>/acatalog">here</a>. </p>
</body>
</html>
<mysite> must be replaced with the web address of your own site.