Yeah previously I names html file home then changed it to index. But why GitHub take only index as right file name, name can be changed?
I don’t know if GitHub allows a different file to be the front page but index stems from the early days of the Web where navigating to a domain or directory would list the files within (similar to exploring a computer’s file system). Most web servers will look for a custom index file (traditionally called
index.html) and serve that to the user instead of a file list.
Technically github pages often hosts Jekyll based sites, and they’re probably configurable. But, indeed, it’s probably better not to spend time trying to defaults.