Are you on localhost..? shared hosting server..?
Care to explain more on your server details.. :)
on localhost try to edit file httpd.conf found in "C:\Windows"
search for line
#LoadModule rewrite_module modules/mod_rewrite.so
and remove # to activate rewrite module, restart your PC and try to learn basic rules for htaccess like
Options All -Indexes # prevent user from viewing folder content RewriteEngine on # switch rewrite ON RewriteRule ^(.*).html$ $1.php #convert any php page to html page in url address
as @minitauros mentioned try to read a guide for making htaccess file