You never have to. After you book with Hotwire, we'll send you a confirmation email. Print that email and take it with you to the airline counter or kiosk. Show them the email and your government-issued ID and they'll give you your boarding pass. Most airlines will also allow you to check in online 24 hours in advance of your scheduled departure to obtain/confirm your seat assignments and obtain boarding passes. You'll need the confirmation number provided in your confirmation email. Instructions can be found on the individual airline's website.
We strongly recommend that you verify the status of your flight on the day of departure. You can check for last-minute delays by either calling the airline or checking the airline's website -- there's a link to it in your confirmation email.