Where to place and organize VBA code for users from other computers to use?

[expeo]

I am attempting to build an interactive document where users can pick from a drop down and a display would show up based on the item picked from the drop down.

Sub ComboBox1_Change() ‘this would be the drop down menu for the user to choose from.
With ComboBox1
.AddItem "AA"
.AddItem "BB"
.AddItem "CC"
End With
End Sub

Sub TextBox1_Change()
If ComboBox1.Value = "AA" Then
TextBox1.Text = "11"
ElseIf ComboBox1.Value = "BB" Then
TextBox1.Text = "22"
ElseIf ComboBox1.Value = "CC" Then
TextBox1.Text = "33"
End If
End Sub

I am having a hard time understanding where to write the code if this document will be passed around (via email) so that all users from different computers can use it.

Would I need to create a UserForm under Forms? Have it under Microsoft Objects? Have it defined as Macros in Modules?

Extra Questions
If this is going to be placed inside Word, can I possibly link it from Excel (to extract data or validate data)?
What would be the difference between Private Sub, Public Sub, and Sub?

 

[Fluff]

Cross posted https://www.excelforum.com/excel-pr...-from-other-computers-to-use.html#post4833254

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[Jon Peltier]

You've shown us code from UserForm controls. So I guess it belongs in a UserForm. What happens once you've populated the textbox? Does something then get put into the document (and what kind of document)? Or is it only displayed in the form and it goes away when the user closes the form?

This sounds like the kind of thing that add-ins are good at.