In order to use System.DirectoryServices classes, you will need to first add a reference to System.DirectoryServices.

Imports System.DirectoryServices is required at the very top of your VB.NET code.

Function GetUserProperties(ByVal GetUser, ByVal Result)
        Dim objSearch As New DirectorySearcher
        objSearch.SearchRoot = New DirectoryEntry("LDAP://dc=domain,dc=co,dc=uk")
        objSearch.Filter = GetUser
        'cn = Full Name, givenName = First name, initials = Middle names, sn = Surname, mail = email address
        objSearch.PropertiesToLoad.AddRange(New String() {"cn", "giveName", "initials", "sn", "department", "mail", "Manager"})
        Dim objResult As SearchResult
        objResult = objSearch.FindOne()
        GetUserProperties = (objResult.Properties(Result)(0))
End Function

Replace dc=domain, dc=co, dc=uk with your AD settings.