What file displays when somebody browses my website in Linux?
When any visitor of your website enter your domain name in to web browser of their system they are immediately pointed to website of your’s default file. To give an instance to visit Yahoo or other website, as a user we need to type Yahoo.com or xyz.com. It does not appear in our web browser, but in actual we are looking at the index.html or index.php page. You can try it from your end just enter yahoo.com/index.html in your browser from your system.
After trying it you might have judged, index.html is a default file of your website. Suppose it is one and only default file in the root folder of your website it automatically shows when somebody access your domain name in their browser.
Although if you have more than two or more files in the root directory, the web server determines which of the file takes priority and then shows that related file.