what does this .htaccess script do?

I found a generator wich creates .htaccess URL rewrite and it created this code:
Options +FollowSymLinks
RewriteEngine on

RewriteRule -ctg-(.*)/ catagories.php?ctg=$1

the only problem is I don't know how to use it, please help me.

thanks.

You just make a file onto the main folder of your website called ".htaccess" and paste the code into it.

You just make a file onto the main folder of your website called ".htaccess" and paste the code into it.

I know already how to use .htaccess :).
but I don't know what does this does with my catagories.php file.