Typically, Catholic colleges will allow anyone to submit an application, so there are no strict requirements about what kind of person can apply-except perhaps requiring that applicants have completed high school. However, there are requirements as to what needs to be submitted by an applicant.
Applicants of a Catholic college are required to submit a completed application, SAT/ACT scores (depending on the college), a high school transcript, and letters of recommendation. With the completed application, applicants should have written in entirety whatever essays were required of the college(s). Some Catholic colleges may also require some sort of statement of faith, though that is growing less common among catholic colleges.
Most applications will also include an application fee, which students will have to pay before their application can be submitted.
While a minimum GPA requirement is hard to pin down, a typical acceptable range is between 2.5-4.0. A lower GPA than 2.5 won't necessarily prevent a student from applying to a university, but it will more than likely affect the decision of the admissions department. More Prestigious Catholic universities will have even higher GPA expectations, so students should be sure to do their research on the academic expectations of the university.