Web crawler

I am attempting to build a web crawler and was wondering where to start? I already have a function that can return a List(Of String) of all the links on a page.

vb Code:

Private Function getemailsfromhtml(ByVal html As String) As List(Of String)
 
        Dim output As New List(Of String)
        If html = "" Then
            html = " "
        End If
        Dim s As String = "([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})"
        Dim m As MatchCollection = Regex.Matches(html, s)
        For i As Integer = 0 To m.Count - 1
            output.Add(m(i).ToString)
        Next
        Return output
    End Function