Someone will hand you a bottle of water as you make your way through the chute. Drink it in small sips. Even if you didn't have to cope with heat and humidity during the race, you lost fluid, so get started putting it back. If there is a sports drink available, have one of those, too.
Keep moving for a few minutes before finding a place to stretch your tight muscles. You will regret it if you head for a chair or bench and sit right away. Those tight muscles will get tighter, and you may be shocked at how hard it is to get up. As you stretch, make sure you target the hamstrings, quadriceps, glutes, and anything else that feels tight.
A Stretch in Time
There will be distractions. You may want to share your triumph with friends and family, perhaps call home and tell someone how you did. That's okay, but try to do your stretching during the first thirty minutes after your race.
You can do a light jog if that helps you get loose. You were probably pushing pretty hard at the end of your run, so whatever helps you relax will be beneficial. Remember, stretching is more effective when the muscles are still warm.
It might not occur to you to do this, but getting back in the water for a few minutes can help you cool down, stave off a bit of muscle soreness, and promote faster recovery of the muscles.
It always feels good to immerse your legs in cool water after a hard run — spraying your legs with a hose works, too — and no matter how warm the ambient temperature, the lake water will feel cool and soothing. It is not necessary to do a lot while you're in the water. Go in to the point that the water hits your waist, then relax as you move around slowly, letting the water do its tricks on your legs. You will have company. There will be plenty of experienced triathletes in there with you.
By the time you have had a drink, a stretch, and a dip in the lake, you can go and check the leaderboard to see how you did. If your race was chip timed, the results will be posted pretty quickly and will include your times in the swim, ride, and run. The results will also include how long you took in the two transitions.