What should be called the lower part of a door cover or pass that is similar to kicking people? Is there a difference between the material of decorative board and decorative board?

You mean the seams between the floor inside and outside the door and under the door? It's a decorative T-button. If it is flat inside and outside, you can also use flat buttons, mostly copper strips and some plastics, which can be glued or nailed with small nails.

I just saw the picture you added. In fact, the door cover landed directly, just like my friend downstairs said. You can't say there is something wrong with your drawings. Maybe you have your own higher decoration effect, but this is a bit superfluous.