i deleted all of the directories that came when i started my site. now invision wont install everything says 404 not found.

Chances are you'll need to terminate your hosting - and reapply. Unless buffalo will be able to restore your files for you.

Buffalo/Opaque may be able to give you an alternate solution, don't terminate just yet.

why did those files matter anyways?

I'm guessing they matter so that your site doesn't get all messed

It's a good thing that it's not hard to gather up the new credits and get hosted again though, if that's what you need to do. Luckily it's not like you already had put masses of work into your site and then accidentaly deleted it all or something. It's easy to start over when you are just starting out.

Best of luck with your new site though!

"All those files" are required by the Apache web Server to control your account and it contains things like who can access what.
By eliminating them, there is no access allowed by anyone, including you. That is a feature of the Apache server software which makes it one of the most secure servers available on the web. Unless access is specifically allowed, there is no access, period.
Read up on the Apache Directives and you will understand how they work. Basically, by deleting all those files and folders, all access is now denied to your account.
Admins may be able to restore them, but maybe not.

Files cannot be restored if you use FTP.

If files were deleted using cPanel, you can always restore them by going to the recycle bin (unless you performed empty of your recycle bin).

When you "mess" with default file settings for your hosting account, admins cannot undo it for you. The only way is to terminate and request for another one.

When you become hosted, there are only 2 files you should EVER deleted.

-Postinfo.html (the default page stating your account is active(I believe))
And
-images (IN /public_html) Those are just for the postinfo.html page.

You may be able to delete index.php, if it's giving you problems. But that's your your /usr folder, so I don't think you should need to. Unfortunely that means you'll need to terminate and re-apply, like buffalo stated. After you're done setting up your hosting account again, PM me if you need help. Don't want you to delete something again .

Is there some ways of making the other directories undeletable (if that's a word?) by users who may accidentally get rid of them or not realise their significance and delete them to free up more space?