3D computer graphics employ the same principles as 2D vector artwork but with an additional axis. The basic objects used in 3D mesh modeling are vertices (points in 3D space) and edges (lines connecting two vertices). Polygons like triangles and quads are formed from edges and vertices and are the most common shapes used in polygonal modeling. A group of connected polygons sharing vertices is referred to as a mesh or wireframe model.

1. Geometry Theory
3D computer graphics employ the same principles found in 2D vector artwork, but use a further axis.
When creating 2D vector artwork, the computer draws the image by plotting points on X and Y axes
(creating coordinates) and joining these points with paths (lines). The subsequent shapes can be filled
with colour and the lines stroked with colour and thickness if required.
Cartesian co-ordinates system
https://www.youtube.com/watch?v=RrrYInyIEGo
Geometric theory and polygons
The basic object used in mesh modelling is a vertex, a point in three dimensional spaces. Two
vertices connected by a straight line become an edge. Three vertices, connected to each other by
three edges, define a triangle, which is the simplest polygon in Euclidean space. More complex
polygons can be created out of multiple triangles, or as a single object with more than 3 vertices.
Four sided polygons (generally referred to as quads) and triangles are the most common shapes
used in polygonal modelling. A group of polygons, connected to each other by shared vertices, is
generally referred to as an element. Each of the polygons making up an element is called a face.
In Euclidean geometry, any three non-collinear points determine a plane. For this reason, triangles
always inhabit a single plane. This is not necessarily true of more complex polygons, however. The
flat nature of triangles makes it simple to determine their surface normal, a three-dimensional
vector perpendicular to the triangle's surface. Surface normal are useful for determining light
transport in ray tracing.

2. A group of polygons which are connected by shared vertices is referred to as a mesh, often ferred to
as a wireframe model.
Primitive
The term geometric primitive in computer graphics and CAD systems is used in various senses, with
the common meaning of the simplest (i.e. 'atomic' or irreducible) geometric objects that the system
can handle (draw, store). Sometimes the subroutines that draw the corresponding objects are called
"geometric primitives" as well. The most "primitive" primitives are point and straight line segment,
which were all that early vector graphics systems had.
Surfaces
surface, In geometry, a two-dimensional collection of points (flat surface), a three-dimensional
collection of points whose cross section is a curve (curved surface), or the boundary of any three-
dimensional solid. In general, a surface is a continuous boundary dividing a three-dimensional space
into two regions. For example, the surface of a sphere separates the interior from the exterior; a
horizontal plane separates the half-plane above it from the half-plane below. Surfaces are often
called by the names of the regions they enclose, but a surface is essentially two-dimensional and has
an area, while the region it encloses is three-dimensional