That’s okay, your English is quite good. I’m saying that the engine will normally only display one side of the polygon, the side that appears a lighter colour in Blender. So the sides that appear blue, will not display properly in the engine.
So in Blender, you’ll need to “flip” the normals, which is the direction the polygon is facing, so that the side you want to see isn’t that blue colour. That way it will appear the same when you import it into Unreal.