If I understand correctly, you need the coordinates of the face border ?
If yes, from the face, get the edges, and from each edge, get the vertices coordinates
Yes, its correct)
But how do i get the edges? Do I need to select them separately? Or can I get them from the selected face? And how can i get the vertex coordinates? Sorry for so many questions, I'm really just learning)
From face, use GetEdges method: Edge edges = face.GetEdges()
For each edge, use GetVertices methods: GetVertices(out Point3d vertex1, out Point3d vertex2).