Techie questions for web-developers/designers (details inside)

Okay, I’ll try to type this in a reasonably coherent manner :)

Say I have a website and an issue with where pages “land:”
If I have xx.domain: I know that if I place a file called “index.html” in any given folder, the browser will default to that page, so if I have xx.domain/index.html, if will automatically load that page – that’s good. But suppose I want to have the main page named something else – say xx.domain/index-main.html. How can I default to that page? If it doesn’t, then I get a generic list of all the files in that given directory: that’s bad.

Do I need some special code? I’m just a plain HTML & CSS guy, so I don’t know if there’s some special scripting? Do I work with my hosting company? It would also be ideal if I can prevent someone from going into my “images” directory? Is that something I can do with this magic coding, too?

Thanks and I can explain in more detail if need be!