Whenever you do your online check-in, after you complete the process, the boarding pass is automatically sent to your registered mail-id. Then you can take a printout it. Otherwise, if you do the check-in at the airline kiosk in the airport, you will be provided with a boarding pass there only.
Spirit Airlines Flight Check-In FAQ's
1. How to get the required boarding pass? +
2. When do I need to reach the airport to catch flight safely? +
Passengers are requested to arrive at least two hours before the departure time of domestic flights. The same is three hours before the international flight departure time.