First time installing grav using the grav-admin donwloaded on a shared hosting and it was on PHP 5.6 - the error page shows up and says that using 5.6 is “too advance?”
and when switching to PHP 5.5 a new error comes up and says
"The requested URL /grav/admin was not found on this server."
searching the folders, one cannot find “admin” folder
Well the error saying PHP 5.6 is too advanced, is quite strange as Grav supports PHP 7 from a very long time, too. Do you have a screenshot of that error? Is this the latest Grav?
For the 404 error, make sure you copied .htaccess to your server too