PHP is enabled in free hosting. One size fits all. You do not have your own php.ini and you cannot change the version on the free account.
But some of the functions have been disabled for security and resource usage reasons. There are often work-arounds. They will not enable a feature just for one account (but you can try lobbying the Admins to enable it for everybody). Try using the Search facility first. There are usually posts about the disabled features. Programming Help is the Forum to post your PHP programming questions.
You can also look around Tutorials
You can use PHP here. Also MySQL, which can be used for many different PHP layouts. Such as Drupal or Wordpress. You should probably take a look at that.