What is Web.config?

In classic ASP all Web site related information was stored in the
metadata of IIS. This had the disadvantage that remote Web
developers couldn’t easily make Web-site configuration changes. For
example, if you want to add a custom 404 error page, a setting needs
to be made through the IIS admin tool, and you’re Web host will
likely charge you a flat fee to do this for you. With ASP.NET,
however, these settings are moved into an XML-formatted text file
(Web.config) that resides in the Web site’s root directory. Through
Web.config you can specify settings like custom 404 error pages,
authentication and authorization settings for the Web sitempilation
options for the ASP.NET Web pages, if tracing should be enabled, etc.
The Web.config file is an XML-formatted file. At the root level is
the tag. Inside this tag you can add a number of other tags, the
most common and useful one being the system.web tag, where you will
specify most of the Web site configuration parameters. However, to
specify application-wide settings you use the tag.
For example, if we wanted to add a database connection string
parameter we could have a Web.config file like so.

Creating a Key Pair?

You can create a key pair using the Strong Name tool (Sn.exe). Key
pair files usually have an .snk extension. To create a key pair At
the command prompt, type the following command:
sn k
In this command, file name is the name of the output file containing
the key pair. The following example creates a key pair called
sgKey.snk.
sn -k sgKey.snk