In any web application, there will be a web.xml
in the WEB-INF/
folder.
If you dont have one in your web app, as it seems to be the case in your folder structure, the default Tomcat web.xml
is under TOMCAT_HOME/conf/web.xml
Either way, the relevant lines of the web.xml are
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
so any file matching this pattern when found will be shown as the home page.
In Tomcat, a web.xml setting within your web app will override the default, if present.
Further Reading