Students wishing to take the ACT go to www.actstudent.org and register
Another great free resource is https://academy.act.org/. This is a great site to go to as a resource and test prep. There are quick quizzes to help you assess your strengths and weaknesses. You can watch as you improve and get better.
For other great resources regarding the ACT including ACT test prep go to http://www.act.org/content/act/en/students-and-parents.html#.