if your page is on your website now, you can just link it and we can look at the html + css! if not, you can copy and paste it in the forum as a code block (the button between “block quote” and “upload image”). it’s hard to tell just from a picture what might be going wrong! (especially since i don’t see any iframes in your picture haha)
perhaps you could also link what w3schools tutorial you’re using? there’s several different ways to do columns in html+css, so the fix depends on what method you’re using.
it sounds like you might need a more basic overview of HTML + CSS than the one you’re using - there’s a bunch linked in the resources list!
it doesn’t reaaaaally matter what order you write your code in, but i think it’s best to do the HTML and CSS simultaneously so you can tell if everything is doing what it’s supposed to do and notice when something goes wrong.