When you set the correct HTTP caching headers, you get a double win because revisits to your web pages load faster and there is less load on your web server. You can read more on HTTP caching: http://code.google.com/speed/articles/caching.html
Even the Apache website gives excellent examples.
a. http://httpd.apache.org/docs/2.0/mod/mod_expires.html
b. http://www.askapache.com/htaccess/speed-up-sites-with-htaccess-caching.html
HTTP caching is complicated only if you make it so. Read the documents patiently and you will be able to create your own HTTP caching code. If you are not sure about handling your .htaccess file,
a. Ask a person who does or
b. Keep a backup of the htaccess file & replace immediately if something goes wrong.
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