SelectedIndexChanged To Open New Form

I have a datagrid view on a page that I'm making and I want to be able to open another form when a user "selects" an entry. I've tried looking through the documentation on how to do that but can't seem to find any. Does anyone know of an easy way to accomplish this task?

Imports System.Data.SqlClient
Imports System.Data
Partial Class _Default
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
TimeDateLabel.Text = String.Format("Today's date is {0:F}", DateTime.Now)
End Sub
Protected Sub whosoncallButton_click(ByVal sender As Object, ByVal e As System.EventArgs) Handles whosoncallButton.Click
Dim dt As New DataTable
Dim da As New SqlDataAdapter
Dim cmd As New SqlCommand
Dim connectionString As String = "Initial Catalog=mdr;Data Source=xxxxx;uid=xxxxx;password=xxxxx"
Dim con As New SqlConnection(connectionString)
con.Open()
cmd.Connection = con
cmd.CommandType = CommandType.StoredProcedure
cmd.CommandText = "getoncall"
cmd.Parameters.AddWithValue("@subschedule", TextBox1.Text)
Try
da.SelectCommand = cmd
da.Fill(dt)
GridView1.DataSource = dt
GridView1.DataBind()
con.Dispose()
Catch ex As Exception
Response.Write("Error:" & ex.ToString)
End Try
End Sub
Protected Sub clearButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles clearButton.Click
TextBox1.Text = ""
GridView1.DataSource = Nothing
GridView1.DataBind()
End Sub
Protected Sub GridView1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles GridView1.SelectedIndexChanged
End Sub
End Class

and what I'm trying to do is that when users click on the SelectedIndexChanged that it takes them from this form with the item that was selected carried through to the next form, and opening a form called messageform.aspx.vb.