This is how:
Public Sub MatePointConstraint()
' Set a reference to the assembly component definintion.
Dim a As Application
Set a = ThisApplication
Dim b As AssemblyDocument
Set b = a.ActiveDocument
Dim c As AssemblyComponentDefinition
Set c = b.ComponentDefinition
Dim p As Point
Dim w As WorkPoint
Set p = ThisApplication.TransientGeometry.CreatePoint(0, 0, 0)
Set w = b.ComponentDefinition.WorkPoints.AddFixed(p, False)
Dim oObject As Object
Dim cmd As CommandManager
Set cmd = ThisApplication.CommandManager
Set oObject = cmd.Pick(kAllPointEntities, "Pick a feature")
Dim oAsmCompDef As AssemblyComponentDefinition
Set oAsmCompDef = ThisApplication.ActiveDocument.ComponentDefinition
' Set a reference to the select set.
Dim oSelectSet As SelectSet
Set oSelectSet = ThisApplication.ActiveDocument.SelectSet
' Get the two entities from the select set.
Dim oBrepEnt1 As WorkPoint
Dim oBrepEnt2 As Object
Set oBrepEnt1 = w
Set oBrepEnt2 = oObject
' Create the insert constraint between the parts.
Dim oMate As MateConstraint
Set oMate = oAsmCompDef.Constraints.AddMateConstraint(oBrepEnt1, oBrepEnt2, 0)
End Sub
Groetjes,