There is a lot of information in the Apache manual about those things, though not in a very readable quality:
htdocs/manual/configuring.html
All directives, which is certainly the source of your problem, are discussed here:
htdocs/manual/mod/core.html
Now about this directive:
<Directory /usr/local/httpd/htdocs>
Options Indexes FollowSymLinks
</Directory>
Here is what the manual says:
<Directory> means that all directives included here are only applied to a certain directory (there are a couple of other directives that can enclose directives).
The "Options" directive controls which server features are available in a particular directory.
"Indexes": If a URL which maps to a directory is requested, and the there is no DirectoryIndex (e.g., index.html) in that directory, then the server will return a formatted listing of the directory.
"FollowSymLinks": The server will follow symbolic links in this directory.
You should look that this is not set for the directory where you want to have your index file read by Apache.
I'm not an Apache expert - I don't know why Apache would not look for index.html if you have the directive set as pointed out and do not override it with a location based directive in the http.conf or in another .htaccess file.