Do I need to buy my ticket online prior to the day of traveling or can I walk in by my ticket same day

You can get a ticket the same day if some seats are still available. It's best to buy ahead a day or so online. But you can still walk in and purchase a same day ticket.

If you buy you're ticket on line and a week or two ahead of travel its cheaper on line.If you are disabled or senior you can get cheaper on line.

I always got mine when I got to the terminal

Same day