<html> <head> <title></title> </head> <body> <div style="position: absolute; left: 100px; top: 20px; width: 100px;"> Sidebar </div> <div style="position: absolute; left: 200px; top: 20px; width: 700px;"> Main content </div> </body> </html>
HTML is markup, CSS is to make that markup look good. As a bonus you get the <div style=""> thing which lets you lay things out perfectly. This is how layout is done with CSS. The layout is being laid out using the style attribute, which is CSS.
You can also use class="" and define a style class in a separate CSS document which you include on each page. This will let you have many pages all with the same layout, and you can change the layout by simply changing one CSS file.
Also. if w3schools isn't to your liking. Try webmonkey. You can google that to find the URL.