htaccess

A htaccess file is kind of an extension of the httpd.conf.
htaccess file can override some httpd.conf control what are .htaccess files are well know for password protection
and mod rewrite rules.

The file itself starts with a period in front of like ".htaccess".  
The file can be open by a text editor because its just a text file.

Please note:
That the Windows and Apple operating systems do not like the dot or period in front of a file.
In other words if you try adding a period to the front of any file both will give an error. ".htaccess" needs the period in front to work.
This can be achieved by using a text editor to save the file name to ".htaccess".

With the Apple operating system the period in front of a file is a system file.
The Apple OS X operating system will not let you see the file at all.
So the only way to open the file ".htaccess" is keep two copies one "htaccess.txt" the other".htaccess" then overwrite changes from the "htaccess.txt to the ".htaccess" file via a text editor.
You should not keep htaccess.txt files on a public web server for security reasons.

More information on the Apache web server can be found at the link below.
http://httpd.apache.org