From Earth, Jupiter appears to the naked eye as a very bright, steady, whitish-yellow "star" — in fact it's typically the third-brightest object in the night sky after the Moon and Venus (and it can occasionally rival or exceed Venus's brightness depending on their positions relative to Earth). Unlike twinkling stars, planets like Jupiter shine with a fairly steady light because they appear as tiny disks rather than true point sources, though atmospheric turbulence can still cause some shimmer near the horizon.
To the unaided eye, Jupiter looks like a plain bright point of light with no visible detail. Binoculars reveal it as a small disk, and if held steady (or mounted on a tripod), you can often spot up to four tiny points of light lined up near it — these are its largest moons, Io, Europa, Ganymede, and Callisto, known as the Galilean moons, first observed by Galileo in 1610. Their positions change noticeably from night to night as they orbit the planet.
With a small telescope, Jupiter shows a visible disk with subtle banding — alternating light and dark cloud bands running parallel to its equator, caused by high-speed winds and differing cloud compositions. A modest to mid-sized telescope under good conditions can also reveal the Great Red Spot, a giant, centuries-old storm, when it's rotating into view (Jupiter's fast ~10-hour rotation means features shift position quickly). Larger amateur telescopes with good optics and steady atmospheric "seeing" can show finer cloud detail, subtle color variations, and moon shadows transiting the planet's face.
Jupiter's appearance also changes with its position in the sky: it's brightest and largest-looking (though still just a bright dot to the naked eye) around "opposition," when Earth passes between the Sun and Jupiter, roughly once every 13 months. At other times it appears dimmer and smaller as the Earth-Jupiter distance increases.