The convention is to use capital Roman letters but it is YOUR polygon. You can refer to the vertices by number, your favourite bands, or allocate an animal species to each vertex or whatever else takes your fancy.
There is no polygon with this name.
A polygon is a closed figure bounded by sides only. Triangle is the polygon of 3 sides and 3 vertices.
pentogon
A polygon has the same quantity of vertices as it has interior angles.
A polygon with 9 vertices is a nonagon.
Hexagon.
There is no polygon with this name.
It is a quadrilateral.
HEXAGON
Just think
A polygon is a closed figure bounded by sides only. Triangle is the polygon of 3 sides and 3 vertices.
A quadrliateral (or quadrangle).
pentogon
The vertices are the "points" of a polygon.
A triangle has fewer than 4 vertices.
Divide the number of vertices by 3. Find the name of the polygon with that many sides. The prism has that polygon as a base. For example, a prism with 24 vertices. Divide by 3 so that is 8. An 8 sided polygon is an octagon. The name is an octagon-based prism.
An hexagon