I'm getting started with Flex and I want to know how can you
publish your project in the web. Instead of using Index.html you
need to use .mxml (main) or you have to add it as a component in
the HTML file.
You can't just put mxml files on the web unless you are using
LifeCycle Data Services (formerly Flex DS), which allows you
compile when the app is requested. So if you aren't using LSDS, you
need to compile the MXML to a SWF and either wrap it in an HTML
file, or access the SWF directly (not the preferable way).