I can give you a brief run down of how php works and where to find the best information. But there will be a lot of needed leg work on your part to get a good comprehension of how to use php. I will bold words that will be good search terms in most search engines.
PHP is a Server-Side language. This means that all the processing of the code is done on the server not the clients machine. If you want to develop on your local machine some good software packages that are free would be:
WAMP, XAMP, Apache2triad. I am sure there are several others, but I have had experience with WAMP and Apache2triad. Those seemed to work well form me. Others my have different opinion. If you are serious about becoming a PHP programming, I would do some research on which books are the best and buy a good PHP book. You should also be able to find some good tutorials online as well.
Once you get started if you run into any problems let us know and we can try to help.