I need someone to explain to me exactly how this code works. Please help

I got this code from an expert. The program permutates all the letters of a phone number input. The program works great but i need help understanding it so if someone could help that would be great!
Public Class Lab4
    Public Function makeCharList(ByVal chars As String) As List(Of Char)
        Dim charsList As New List(Of Char)()
 
        For Each c As Char In chars.Trim().ToCharArray()
            charsList.Add(c)
        Next
 
        Return charsList
    End Function
 
    Private Sub generate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles generate.Click
        'Use of a dictionary may be better, it uses same concept as KeyValuePair but already has it in a collection
        'Therefore, you will not have to recreate the wheel
        Dim dict As New Dictionary(Of Char, List(Of Char))()
        Dim words As New List(Of String)() 'To store word possibilities
        Dim wordsTemp As New List(Of String)() 'Temp word lists as needed
        Dim listTemp As New List(Of Char)() 'Temp character list
 
        'Adds and assigns each digit to an array of characters
        dict.Add("0", makeCharList(""))
        dict.Add("1", makeCharList(""))
        dict.Add("2", makeCharList("ABC"))
        dict.Add("3", makeCharList("DEF"))
        dict.Add("4", makeCharList("GHI"))
        dict.Add("5", makeCharList("JKL"))
        dict.Add("6", makeCharList("MNO"))
        dict.Add("7", makeCharList("PQRS"))
        dict.Add("8", makeCharList("TUV"))
        dict.Add("9", makeCharList("WXYZ"))
 
        Dim phoneNo As String = phonenumber.Text.Trim() 'assigns value of textbox control to local variable
 
        'Goes through each digit of your phone number
 
        For Each digit As Char In phoneNo.ToCharArray()
 
            listTemp = dict(digit)
            If listTemp.Count > 0 Then
                '''''''''' setup words list ''''''''''
 
                wordsTemp.Clear()
                If words.Count < 1 Then
                    wordsTemp.Add("")
                Else
                    wordsTemp.AddRange(words)
                    words.Clear()
                End If
 
 
                For Each word As String In wordsTemp
                    For Each c As Char In listTemp
                        words.Add(word & c)
 
                    Next
                Next
            End If
        Next
 
        MsgBox(String.Format("Writing {0} words to list", words.Count))
        lbWords.Items.Clear()
        lbWords.Items.AddRange(words.ToArray())
        MsgBox("Generate process complete!")
 
 
    End Sub
 
End Class

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ajh305Asked:
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MysidiaConnect With a Mentor Commented:
It seems self-explanatory.  

The code declares and sets up  'dict'  a hash indexed by the digits 0 through 9,
with a stored value of the letters  associated with that digit
i.e.  "2" to "ABC"
...

Next a variable 'phoneNo'  is assigned to the current value of a textbox at the start of the procedure.

A temporary list "words" starts in the empty state.

A for loop examines each character.
  Within one iteration of the for loop
   the digit is examined

   'listTemp'  is assigned to the list of characters from "dict"
    i.e.  if    the current digit is "2"  then  listTemp  is the list with 3 items,
    A, B, C,
    if current digit is "3"  then  listTemp  is D, E, F,  and so on.

    A temporary list  "wordsTemp"   is reset so it contains no items.

    If there are any items in the "words"  temporary list, they are added to wordsTemp
    and  "words" is again reset to an empty state.

    For every word in the  "wordsTemp"  list
       For every item in the "listTemp"  list of characters
          the word in wordsTemp   PLUS the character in listTemp
          is added to the "words"  list
         

    The iteration of  the outer 'for' loop completes and the next digit is now being examined.

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