You mean publish.
With iWeb 08 you can only publish to a folder.
Where you publish, or save that folder, is up to you.
You have to remember that.
Then you use a 3rd party FTP application to upload that folder + the index.html file to the webserver.
With iWeb 09 you can also directly publish to the server with FTP.
Your webhost will tell you what your username, password, serveradress and pathname are.
And please browse this forum. You question is dealt with several times a day.
Your first post shows that you use iWeb 08.
If you have iWeb 09, click the Sitename and then choose from the popup menu where you want to publish.
Then choose Publish from the File menu.
If nothing is changed then the Publish command/button is greyed-out.
If you use iWeb's FTP, then your earlier question about where iWeb saves in the Finder and how to upload the folder is irrelevant.