1) Five planets are visible to the naked eye: Mercury, Venus, Mars, Jupiter and Saturn. Looking just once at the sky, it is hard to tell a planet from a star. The planets rise and set with the stars. But observed carefully, over several days or weeks, the planets change their places relative to the stars. The stars are sometimes called "fixed" (i.e.,not moving) stars, to distinguish them from the "not fixed" (moving) planets. The planets don't wander just anywhere in the sky; they stick pretty close (within 10 degrees or so) to the ecliptic. The part of the sky around the ecliptic is called the Zodiac. The constellations of the zodiac (the "what's your sign?" constellations Gemini, Cancer, Leo, Scorpio, etc.) are strung out along the ecliptic. Each occupies a sector 30 degrees wide. At any specific time, each planet is "in" one and only one of the zodiacal signs. Unlike the sun and the moon, the planets don't just move west to east, relative to the stars, a certain fixed number of degrees every day. Rather, they move sometimes west to east, sometimes east to west, in a complex way. Until the 18th century, the explanation and prediction of the motions of the planets, together with eclipse predicting, was probably the main business of astronomers.
2) Two of the more easily observed regularities of planetary motion are:
(a) A planet is "in conjunction" with the sun when it lies in the same line of vision as the sun, as seen from earth. (i.e., it's directly in front of, or directly behind, the sun.) The time between two consecutive conjunctions is called a synodic period. For example, the synodic period for Jupiter is 398 days, and for Venus is 586 days. (In physics, motion which repeats itself is called ``periodic'' and the length of time it takes to return to its starting point is called its ``period''. Astronomy uses the same word.)
(b) Mercury and Venus are never very far from the sun in the sky. They either set soon after the sun, or rise just before it. These are called "evening stars" (if they set soon after the sun) or "morning stars" (if they rise just before the sun). These two planets are never visible in the night sky for more than a few hours at a time. The other planets may be up at any time.