If you've created a Master Page, to create a new Web Form you can just by the following clause:
<![CDATA[<% @ Page Language = "vb" AutoEventWireup = "false" CodeBehind = "CadMetasLoja.aspx.vb" Inherits = "SAC_BESNI.ConsMetasLoja" MasterPageFile = "~ / MasterPrincipal.Master"%>]]>