怎么将上面和下面连起来？

[copywzy]

怎么将圆圈的下面和方框的上面连起来？

[arroniow]

@copywzy

How do you connect the bottom of the circle with the top of the box?

Is this what you mean?
A Box to Tube Loft.

[TheBum]

Make the top a solid cylinder and the bottom a solid block, use the Loft tool, and then use the Shell tool to hollow it out.