Newbie question: Basic knowledge

Hi there! I'm really newbie and I have a major problem. I think i've installed the PHP stuff correctly, but I don't know how to insert a PHP feature into a ordinary HTML page. Actually i've tried to find it in the faq, but i didn't. so could please somebody tell me how it works, just combining a php file with the source code. If possible, for example to give me a very simple example, so that i can understand the basics! I'm really desperate so please somebody help me! Thanks a lot Christian