I don't know what caching you are looking to implement, but from the sentence it sounds like you want to apply it on the images, css and html. To do that you will need to add the expire times when they are pulled. I.e. Telling the browser that image A is valid for one week from today, that way the browser wont check for an update before a weeks time.
If you want to learn more about content caching, I strongly recommend these two books by O'Reilly.
High Performance Web Sites
Even Faster Web Sites
If you are talking about server side, look into APC or Memcache.
I don't know if your in the web development business, but if you are I strongly suggest that you look into caching again. Caching is simple, easy to implement and beneficial even for smaller websites.
I wont go on about the topic, as there is a lot of different cache methods, systems and approaches all depending on what you want to cache. The important part however is as normal tied down to money, with the system cached, you save server resources (more websites per server for example if its smaller websites), using less bandwidth and so on.