Satellites don’t make their own light — you see them only when sunlight reflects off them toward you. The sweet spot is the hour or two after dusk and before dawn: the satellite, high up, is still bathed in sunlight while the ground below you has already fallen into darkness. In the middle of the night a low satellite is in Earth’s shadow and invisible; in full daylight the sky is too bright.
A “pass” is a single crossing of a satellite over your local sky, described by when it appears, the direction and maximum height (elevation) it reaches, and when it disappears. A high overhead pass is brighter and longer than one that just skims the horizon. Pass times are specific to your location, because the satellite has to be both sunlit and above your horizon at once.
Brightness is reported as visual magnitude, the same backwards scale astronomers use for stars: smaller and negative numbers are brighter. A bright ISS pass can reach magnitude −3 or brighter, easily outshining every star; many satellites hover around magnitude 2 to 4, visible but faint. Freshly launched Starlink satellites can appear as a startling “train” of dots strung along the same track before they spread out and climb.
To tell a satellite from an aircraft: a satellite is a single point of steady light with no blinking and no colored navigation lights, gliding in a straight line and often fading out mid-sky as it enters shadow, rather than flying off beyond the horizon. Find a spot away from streetlights, let your eyes adapt for a few minutes, and look toward the part of the sky the pass prediction gives you.