You have web application settings in the <appSettings> section of your web.config, and you want to access them in Web Form (.aspx) File or Web User Control (.ascx) file, you can use appSettings binding expression as shown in the following code.
Suppose you have following appSettings in web.config
<appSettings> <add key="LoginButtonText" value="Login" /> </appSettings>
You can read above appSettings in aspx or ascx file as follows:
<asp:Button id="Button1" runat="server" Text='<%$ appSettings:LoginButtonText %>'></asp:Button>