change site visitor views

how do i make it so visitors get rerected from site.com to www.site.com so visitors only use the www.site.com

been told that i need to add something to the .htaccess file to make this so.

what is this ?

RewriteEngine on
RewriteCond %{HTTP_HOST} ^site.com
RewriteRule ^(.*)$ http://www.site.com/$1 [R=301,L]

RewriteEngine on
RewriteCond %{HTTP_HOST} ^site.com
RewriteRule ^(.*)$ http://www.site.com/ [R=301,L]

thank you, but how do i get the visitor to be sent to the page they were trying to view first
say they type in

site.com/mypage.html they get sent to www.site.com

Check again the rewrite rule (it needs a $1 after the destination url).

sorry this has gone over my head, all i done was copied to code you gave to the top of my .htaccess page and changed the domain names

where do i put the $1 ?

ok i see i did not have the $1 after the /

RewriteEngine on
RewriteCond %{HTTP_HOST} ^site.com
RewriteRule ^(.*)$ http://www.site.com/$1 [R=301,L]

but still i am always taken to the home page being www.site.com

if i was to visit say

site.com/mypage.html i would like the visitor taken to www.site.com/mypage.html
same for
site.com/anotherpage.html would take them to www.site.com/anotherpage.html

and finally site.com/anotherfolder would take them to www.site/anotherfolder

The rewrite rule is correct. Restart your web server and try again.