You create the .htaccess file yourself, or at least I did with my 1&1 account. The .htaccess file overrides default web server settings for the directory it is stored in.
In plain English, if you have an .htaccess file in one folder on your website the contents of that folder will react to the instructions placed in your .htaccess file, even if the web server is set up with different instructions.
I use them for all sorts of things, from controlling error pages to setting specific PHP attributes to parts of a site by overriding the web server default.
If people only knew just how much you could do with a humble .htaccess file they'd be very, very surprised.
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