Does anyone know of a good guide explaining how to position elements using CSS?

I am coding my first website using HTML and CSS and am having a lot of trouble getting my images to be placed exactly where I want.

I’ve read about the position modes “absolute”, “fixed”, “relative”, etc, but I am unsure which to choose to realize my idea.

My goal is to be able to move my images around my page, pixel-by-pixel, so that they sit exactly where I like. I have yet to figure out how to set up my code to have such freedom of movement. No matter what values I set as “top”, “left”, or whatever, my images do not budge. I am generally confused on this whole aspect of CSS. Any help would be greatly appreciated!