iWeb problem

Hello,
I have brand new iMac, so I am just learning to work with Mac OS. I have tryed to open saved web page html in iWeb and iWeb wrote message "This file is not supported." so I pressed OK and tryed reopen iWeb (without that page). But that wrote again same message. It write that message everytime, when I try to open iWeb. How I can stop iWeb trying to open that page? And which files are supported by iWeb?
could anybody help me?
Thank you

 

I understand that I can open in iWeb only iWeb files.
But now I cant open iWeb anyway. Still comes this message:"Cant open file:..."
I want to open no file, I just want to start iWeb, but I cant.