A vector will be created from the subtraction of two positions. Since it is possible to confuse which point to subtract from, you can use the “vector_to” method. Given an API entity called “edge”, you can use the following statement:
vector = edge.start.position.vector_to( edge.end.position )
Another topic in this forum has discussed pointing a face:
Search for @thomthom’s assignment of “transform_local_to_face”.