If you want to change the default file, you can do it. usally server loop up /public_html directory and Deafult file is index.html
300 - Multiple Choices 301 - Moved Permanently 302 - Moved Temporarily 303 - See Other 304 - Not Modified 305 - Use Proxy
301 ese when the old page has been permanently moved and coming reguest shold be sent to the target page PageRank may be transferred
The requested page has moved temporarily to a new url so page is cached if indicated by a Cache- Control or Expires header field.
Redirect /redirect_old_from.html http://www.example.com/folder/redirect_new.html
Redirect 301 / http://newdomain.com
If you change the directory structure and page have not change. redirect all request to new directory
Redirect 301 /olddirectory http://newdomain.com/newdirectory