Tributes are timed once they enter the Launch Room for how long they have until they need to enter the tube. Tributes are usually guided into their tube by their stylist.
Once the tributes enter the tube, the tube is shut and can not be opened until the tribute enters the arena. The tube also blocks out sound from the Launch Room, as during the Hunger Games film Katniss Everdeen is shown as very scared and banging on the tube.
It is also suggested that they are made of some form of unbreakable material as during Catching Fire Cinna is dragged away and she is shown trying to break the glass, but she fails to. When the tributes enter the arena from the tube they are faced with land mines in front of the launch plate to ensure that the tributes do not step off of their plate before the one minute is up, and if they do, they will be blown up by the land mines.
If a tribute steps off too early, the mines detonate and kill the tribute by blowing them sky-high. The slightest provocation can set off the mines to detonate as well. Once, a tribute dropped her tribute token, a small wooden ball, on the ground before the minute was up and it triggered the land mines which blew her up. Her body parts were "practically scraped off the ground".