when i create roads, I want to create a mesh to fill the road. The mesh maybe like the following picture.How can I do that?
I think what you looking for is spline component, which allows to render mesh along the spline.
https://docs.unrealengine.com/en-us/Engine/BlueprintSplines
https://api.unrealengine.com/INT/Videos/PLZlv_N0_O1ga0aV9jVqJgog0VWz1cLL5f/wR0fH6O9jD8/index.html
this is probably what they used sample you show in photo.