I'm probably not explaining this clearly, so lets try from square one. (I'll try not to insult your intelligence in the process). So, when you request a web-page, the server delivers html that is then displayed in your browser. How that html comes to exist is in one of two ways. A static web page can be made in which everything is hard coded into the .html page. The disadvantage to this is that any time you want to change anything, you have to do it by hand. The advantage is that that it is relatively simple for anyone to put together a web page.
If you look at Bleeping Computer, the content is changing all of the time. When people reply to threads, their content automatically appears the next time the page is generated; stats are continuously updated, etc. Pages are being dynamically generated upon request; ie, they do not exist until you request the page (there are exceptions to this, but lets ignore them for now). When a page is requested, the server looks at what is being requested, and generates the page based on the request and a template. All of the data is pulled from a database and assembled in such a way that you see a web page. PHP is the engine that drives all of that.
The opposite is also true. When you reply to a post and hit the reply button, the text that you entered into the text box is sent back to the server. Once it gets to the server, some application adds it to the database in the correct place. The next time anyone views that thread, the page is generated and now includes your response as part of the new web page. There are many advantages; content is always changing, site-wide changes can easily be made by tweaking templates, little to no human interaction is necessary. The downside is that there is more stuff to know. Although Bleeping Computer is mostly templates, Grinler spends a lot of time tweaking things and adding functionality.
If you want to automatically add comments, you need something on the server that knows what to do with the text (in your case, visitor comments). Whether that be PHP, Java, or any other language, it doesn't matter. As long as it knows what to do with the text. Then, you need some application that can retrieve the data nad dynamically generate the updated web page. Again, the language does not matter.
Did I explain the process better? And more importantly, did I not manage to insult you.