Adding boxes

Hi WordPress users

There’s just one tiny problem before my first website is 100% complete, and I hope you would like to help me with it.

Look here

So I found out, that the yellow box with the content was a #container. I was then able to style it yellow and decide it’s width with CSS. So here comes the problem: How do I add several more of these yellow containers to my website? I would like to add maybe 3 or 4 more of these boxes right to the one with content. I would like to decide each of their size and placement. The boxes should be placed on the white area (see picture above). Is this possible? I’m a real newbie to coding and stuff and would appreciate any help. Thanks.