SetEnv, SetEnvIf, and SetEnvIfNoCase directives conditionally set environment variables accessible by scripts and apache based on HTTP Headers, Variables, and Request information.

A first-time visitor to your page will make several HTTP requests to download all your sites files, but using the Expires header you make those files cacheable. This avoids unnecessary HTTP requests on subsequent page views.

How to password-protect, Allow or Deny a visitor based on a condition. If you are having trouble getting htaccess-based password protection to work see: Troubleshooting htaccess Authentication: Getting it to work

Some good examples for how to use the Files and FilesMatch directives in .htaccess files and httpd.conf files for Apache.

<FilesMatch ".(htm|html|css|js|php)$">
AddDefaultCharset UTF-8
DefaultLanguage en-US
</FilesMatch>

Learning about charset's and file types maybe pretty boring, but using .htaccess it can be fun! Here's a quicklist htaccess cheatsheet for adding the correct Charset to a web document.