目录索引问题

I'm building a php server (testing, I'm a newbie), wrote some code and then tried it. The problem is that the default index is index.html, so I removed it, and then I get this blank page.

Then, searching on the web I found about the DirectoryIndex command, but if I try this one I get DirectoryIndex: invalid command. What have I missed?

Just put

DirectoryIndex index.php (or whatever is your index file)

The DirectoryIndex command cannot be empty. This is the command that tells Apache which file to use as the index file. The server has no preferences by default and hence this is a required directive.