Set default Culture in web.config file

<configuration>
<system.web>

<globalization

    culture="en-US"

    uiCulture="en-US" />
</system.web>

</configuration>

can i have more than one web.config file in one website?

yes, You have more than one web.config file. You can use it as your requirement.

what is Web.config ?

As name suggest web.config is web site configuration file.

Globally configure you website through web.config file.