In your .aspx page you should have something like this...
<asp:Label ID="theLabel" runat="server" />
and then you will be able to do something like this (VB
theLabel.Text = "mytext"
in your source code (e.g. in Page_load).
Be aware that is totally different from Classic ASP, so you might want to buy a book, a read some tutorials online. The basic idea is to seperate HTML from code.
Hope it helps!