There are a myriad of Emerald Pools Trails: Lower Emerald Pools, Middle Emerald Pools, Upper Emerald Pools, and a variety of use trails interconnecting them, usually with some tag as one of the above which can be confusing. The most popular way appears to be: after you cross the bridge from the Zion Lodge bus stop, go right, this is the lower pools trail. When you reach the waterfalls, you can climb around and up to the middle/upper trails. The upper trail is a one way trail to the highest elevation pool where you can view the Heaps canyon exit, which may be a 300 foot waterfall after recent rains. You can make a loop out of all of them for about 2-3 miles total hiking.
Zion Park charges entry fees per vehicle. During the summer they operate a free shuttle system between the visitor center and most hiking trails.