To clarify here, if you want "a search engine" on your site, do as others have suggested here and add the google widget to your page... easy to install and works well.
By mentioning php search engine, you are insinuating that you want to have your OWN search engine... i.e. an indexed set of results + a search function front end. This method is NOT easy and I wouldn't recommend it for the faint hearted.
However, you can install your own php search engine, which will index your own site and provide a good search system. One exists at
www.sphider.eu. I have tested this and it works well.