.htaccess files can sit in any/every directory. Each file applies to the directory it is in and all subdirectories. A lower file will override any higher files.
.htaccess is read on every web request, so changes take immediate effect.
.htaccess uses the same syntax as Apache configuration files, but not all directives valid in the config files is valid here.
[The Ultimate Htaccess]
[Key to directives]
[List of directives]
[Test RewriteCond and RewriteRule Here]
My server throws a 500 error if you use comments at the end of an executed line. So only use full-line comments.
If an argument contains a space, the argument must be enclosed in double quotes (").