Trying to Ad Banners

Hello WordPress community. Im new to the wordpress development. Im currently running a project and I need to add Banners to it. The Banners must be editable by the client. Its one of the most important thing actually. Im decent in HTML and CSS and a beginner in PHP.

I have been trying to make a custom post to add the banners, I also tried adding them with a widget but I keep facing the same problem. Every time a new post is “posted” everything gets pushed down. Even the widgets on the secondary aside and I need them to stay on the same place even if more dynamic content like posts keep increasing.

You can view the site here “https://www.loquehay.mx” (I’m still working a few details).

Besides that I need to put different adds on the different categories, but all on the same place. I manage to do that with CSS but the thing that is making me crazy is that I have no idea how to stop everything from moving down once a new post is published.

Thanks in advance.