If I understand you correctly, you want one textbox on each tab page?
If so, then just declare a new textbox control, set it's properties (font, size, anchoring, docking, etc) and add it to the tab page.
Since you are adding an unknown number of tab pages/textboxes, I suggest creating a method that creates the new tab, adds the textbox, sets any properties, and then adds it. That way you can call that one function as many times as you need.
If you are going to want the textboxes that you add to the tab pages to have events that you code for, you'll also want to add event handlers when you're adding it.
Here is a smaple of code I use to do something similar. But I use a richtextbox instead. I also have three different events that I'm tying to the richtextboxes. I didn't include the code for those, but they would look like any other textchanged, keydown, keypress event for a richtextbox.
Dim tpNew As New TabPage(strTabName)
tpNew.Padding = New Padding(3)
tpNew.BackColor = Color.FromKnownColor(KnownColor.Control)
tpNew.ContextMenuStrip = mnuBuildYourOwn
Dim rtxt As RichTextBox = CType(tpNew.Controls(0), RichTextBox)
rtxt.Dock = DockStyle.Fill
rtxt.Font = gblFont
rtxt.BorderStyle = BorderStyle.FixedSingle
rtxt.ContextMenuStrip = mnuUserText
rtxt.DetectUrls = False
rtxt.AcceptsTab = True
RemoveHandler rtxt.TextChanged, AddressOf richtextbox_TextChanged
RemoveHandler rtxt.KeyDown, AddressOf FieldName_KeyDown
RemoveHandler rtxt.KeyPress, AddressOf ManualSQL_KeyPress
AddHandler rtxt.TextChanged, AddressOf richtextbox_TextChanged
AddHandler rtxt.KeyDown, AddressOf FieldName_KeyDown
AddHandler rtxt.KeyPress, AddressOf ManualSQL_KeyPress
tcBuildYourOwn.TabPages.Insert(tcBuildYourOwn.TabPages.Count - 1, tpNew)
Hope this helps.