You haven't imported them properly, delete everything above the green comment text. So the top of each class looks like this (obviously different for the SHA version):
'*******************************************************************************
' MODULE:       CMD5
' FILENAME:     C:\My Code\vb\md5\CMD5.cls
' AUTHOR:       Phil Fresle
' CREATED:      16-Feb-2001
' COPYRIGHT:    Copyright 2001 Frez Systems Limited. All Rights Reserved.
'
Then in a standard module:
Public Function MD5(s As String) As String

    Static md5Hash As CMD5
    If md5Hash Is Nothing Then Set md5Hash = New CMD5
    
    MD5 = md5Hash.MD5(s)
    
End Function
Public Function SHA256(s As String) As String

    Static sha256Hash As CSHA256
    If sha256Hash Is Nothing Then Set sha256Hash = New CSHA256
    
    SHA256 = sha256Hash.SHA256(s)
    
End Function
Then in D4:
=SHA256(B4)
I4:
=MD5(B4)