How do you change the timeout for a Session object?

You can change the timeout for a Session object by setting its Timeout property or by using the Web.Config file.

Where do you store connection string?

Database connection string can be stored in the web config file.
The connection string can be stored in the WEB.Config file under
element.

Can we have more than one web.config file?

Yes,we can have more than one web.config but in different folder.
In root we can have only one web.config file.

How to get the authentication mode from web.config file programmatically at runtime?

Write following code.

System.Web.Configuration.AuthenticationSection section =

            (AuthenticationSection)WebConfigurationManager.GetSection("system.web/authentication");

Label1.Text = section.Mode.ToString();

You will get the authentication mode set in your web.config file.

What is custom tag in web.config file?

Custom tag allows you to create your own tag and specify key value pair for it.