You just need to feed the AddArc method what it wants. It wants radius and angles. Find the radius by getting the distance between your center and the point you pick. Then calc the angles from your two points...
Sub Example_AddArc()
' This example creates an arc in model space.
Dim arcObj As AcadArc
Dim centerPoint(0 To 2) As Double
Dim radius As Double
Dim startAngleInDegree As Double
Dim endAngleInDegree As Double
' Define the circle
centerPoint(0) = 0#: centerPoint(1) = 0#: centerPoint(2) = 0#
radius = 5#
startAngleInDegree = 10#
endAngleInDegree = 230#
' Convert the angles in degrees to angles in radians
Dim startAngleInRadian As Double
Dim endAngleInRadian As Double
startAngleInRadian = startAngleInDegree * 3.141592 / 180#
endAngleInRadian = endAngleInDegree * 3.141592 / 180#
' Create the arc object in model space
Set arcObj = ThisDrawing.ModelSpace.AddArc(centerPoint, radius, startAngleInRadian, endAngleInRadian)
ZoomAll
End Sub
"Everybody is ignorant, only on different subjects." — Will Rogers