To add a page:

procedure TForm1.Button1Click(Sender: TObject);
begin
    TabbedNotebook1.Pages.Add('Delphi');
end;

Top change the amount of page tabs that are in a row:

procedure TForm1.Button1Click(Sender: TObject);
begin
    TabbedNotebook1.TabsPerRow := 5;
end;

To edit a tab page in Delphi:

Select which tab you would like to change in the TabbedNotebook in the ActivePage property
in the Object Inspector.

To change the tab page during Run-Time:

procedure TForm1.Button1Click(Sender: TObject);
begin
    TabbedNotebook1.PageIndex := 2;
end;