You are looking at this the wrong way around. If you don't understand what PHP is used for, then what is your logic in wanting to incorporate it into your website? Unless your intent is just to learn another language, it is a matter of looking at requirements and then trying to match them up with what PHP or some other language can do. Even if you just want to learn another language, it is a significant commitment of time and effort to do that. You want to be sure that you make the right choice.