Each bar is one world's orbit drawn on a logarithmic distance scale — it runs from its closest approach to the Sun (perihelion) to its farthest (aphelion), with a dot at the average. A wide bar means a stretched, eccentric orbit. Notice how Pluto's orbit actually crosses inside Neptune's.
Orbits are ellipses with the Sun at one focus (Kepler's 1st law). A planet moves fastest at perihelion and slowest at aphelion (2nd law), and the farther out it is, the longer its year — period² grows with distance³ (3rd law), which is why Neptune takes 165 years to lap the Sun while Mercury needs just 88 days. Eccentricity (how oval) and inclination (how tilted out of the flat ecliptic plane) are small for the eight planets, which is why they all track the same narrow zodiac band across our sky.
Rocky worlds first, then the giants — each with its moons, its spin and a few things that stick.