CSS/HTML Help - Auto-size webpage to fit any screen?

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Hi, I need some help with my website. I'm coding it with HTML/CSS and a tiny bit of PHP. I need help trying to make it so it auto fits to any size PC screen, so like I code it on my 19" screen and it's perfect placement (images, text etc. on the webpage), and if I go view it on a 22" screen the placements all stuffed up. Can anyone please help me fix it?*

*I tired using percentage, so please no one say that.
Thanks in advance.