Need some basic help with PHP, for creating header/footer files

I want to use PHP to streamline my site. So I want to take my layout and split it into two halves (header.html & footer.html) then have each individual page request the header and footer via PHP to create the full layout. I don't think this is so complicated, but I'm in the dark about one aspect. That's setting up the head of the header file so that certain information changes accordingly depending on what page you are on. For example the "title" tag would need to change according to what page is loading. Same with certain meta tags.

I hope I explained myself properly, and I hope someone here can give me some detailed examples of how this is done. I must confess I'm a PHP idiot, I don't know much at all, but I've managed to get a few scripts going in the past.

Thanks in advance.