What Does Vector3.new means?

Vector3.new is a function which creates a new Vector3.

In math, a Vector is something with length and direction. It's usually represented as a coordinate, e.g., (4 left, 3 up, 7 backward).

A vector in the elementary sense is an ordered list of numbers; a "Vector3" then is an ordered list of 3 numbers. We call these numbers, in order, x y and z. These three numbers are the parameters to Vector3.new(x, y, z)

Since Vectors define a point in 3D space, we use it for Position of parts.

As well, as some components of CFrame which augments a Vector3 with several other values to define the orientation (rotation) of an object.

Vector3.new sets the new Vector3 value, which is for positioning and CFrame.

Vector3.new is the way to position a GUI (CFrame.new is for parts) using the basic math figures, x, y, and z.