Ok, well for a simple list of the relevant attributes, check out the
Dimension,
Classification, and
Positioning pages at W3Schools, to learn about: width/height, top/left/bottom/right, position, float, clear, display.
Then experiment with them. By way of a very quick explanation:
Most times, I set
margin: 0px; border: 0px; padding: 0px on all layout elements, because otherwise they might trip you up. (But don't be afraid to fiddle with them if necessary.)
Once the above are taken care of, width & height are fairly obvious. Except potentially for small values - if your height is to high, it's usually because of the font-size. Use font-size and line-height to fix with that.
top/left/bottom/right are positional - you need to have
position:absolute; for them to work in relation to the window, though usually using float and clear are better.
Oh, and make sure to set
display:block; on things which might otherwise be inline.
Remember, percentages are in relation to the parent element - so if you set something to width:50% you need to have a valid width on the tag which contains it, otherwise it wont make sense.
So yeah, just go experiment with the above and hopefully it'll eventually become clear. If not you can of course ask specific questions here.
:)