You can't because iCloud does NOT offer web hosting.
If you want to host your site then you'll have to purchase a web hosting account with one of the numberous hosts there are around and you'll also need to register a domain name if you have not already.
iWeb offers two ways to publish your website...
... if you upgrade to V 3.0.4 using the iLfe '09 or '11 disk which is still available from Amazon.
Here is some info about choosing hosting and getting a free domain name...