CSS - 将div推到右浮动内容下方

I'm having difficulty with using float. Now I'm trying let some content float to the right side of the screen and I expect the non-floated content to be below it. However it turns out that the non-floated takes up the left side of the screen. Then I added top margin to the non-floated so that it will be pushed down but it's strange that it doesn't work. I'm having difficulty with using float. Now I'm