Once you are at the trailhead, you have two choices. Either follow the old road to Poiana Brasov, a gravel path that starts on your right before you reach the toilets, or continue past the toilets on a path that then curls to your left as it ascends on a trail named Valea cu Apa. The first option is very steep and offers no water, but there are wild raspberries in July if you have a keen eye. The trail on the left is less steep but >20% longer, and actually ascends to 100m above Poiana Brasov. I prefer it both coming and going because (a) you get a view of the nice canyon walls, (b) it is a less steep descent for those with brakes that are a bit weak, and (c) the spring water < 500m after the start (on your right as you first see the walls) is really good, so you only have to carry enough water to get to the spring, and refill there.
Back to the trail... after at most a few km beyond the spring water, Valea cu Apa continues straight, but a sign points toward Poiana Brasov along a gentle switchback if you take a sharp right turn. Take that switchback and you are on your way to Poiana Brasov. After that, the signage sucks. The first choice you'll have is continuing straight or turning right across a creek. Going straight will take you above Poiana Brasov -- any of the trails are fine as long as you have an actual map or can hear the traffic to get back to the main road. The simpler way is to turn right across the creek, and take the first left. That puts you on the old road that most people take, Drumul Vechi al Poienii.
When that trail reaches the paved highway, turn left, paralleling the highway until the trail dumps you out on Strada Poiana Ruia. Keep going straight (Ruia turns right) on Strada Poiana Ursului until road markings require you to turn right near a minimarket. Ignore that and turn left on Strada Poiana Soarelui. You have a ton of choices for eating, but I just go down to where the church is on the left. On the right is a stand with really good langosi and kurtos kalac pastries. A langosi with jam is heaven if you like sweet, and a kurtos with cinnamon leaves enough left over to snack on cleanly on the way back.