Distance: 8.5 miles (13.5 km) one way
Elevation Range: from 4,000 feet (1,220 meters) on the valley floor to 7,200 feet (2,200 meters) at Glacier Point
Total Elevation Change: 3,200 feet (975 meters)
Official Guide to the Squiggly Lines: The Panorama Trail is the long red line plus your chosen combination of the green line (the John Muir/Half Dome Trail) and the yellow line (the Mist Trail). Assuming you're hiking downhill from Glacier Point, you'll start at the giant green hikers at the far left of the red line and then follow said red line until it intersects with the Muir Trail (green line).
Go left at the red/green intersection to take the Muir Trail. It's a bit longer and not as scenic as the Mist Trail route, but it's less steep. It intersects with the Mist Trail just upstream from the Vernal Fall footbridge.
Go right here to take the Mist Trail the rest of the way to the valley floor. This route will take you directly past Nevada and Vernal Falls and is clearly the more scenic alternative, though it will be more crowded and may not be your choice if your knees are redlining. If you like, you can compromise and take the John Muir Trail just until the purple trail, which skips Nevada Fall but intersects with the Mist Trail just above Vernal Fall.
In any case, the trail ends at the second set of giant green hikers, which are just across the bridge from Happy Isles. If you parked at the trailhead parking lot or at Curry Village (see the two giant "P"s just to the northwest of the trailhead), you can walk there from here; otherwise, you can catch a free shuttle bus from Happy Isles to various points in Yosemite Valley, including the large parking lot at Yosemite Village.
A few notes on some of the other bits of trail that are intruding on your view here: the green line at the far left of the window is the 4-Mile Trail, which, like the Panorama Trail, goes from Glacier Point to the valley floor, but comes out farther to the west. If you're in good shape, taking the 4-Mile Trail up and the Panorama Trail down is one of Yosemite's great hikes.