An observer at the equator will see all of the constellations during the course of one year. The polar constellations Polaris and the Southern Cross appear near the horizon, while the rest pass overhead based on the season.
The Earth’s orbit and axis limit what constellations an observer can see at any given time. Since the axis is always tilted 23 degrees and the Sun shines for half a day, an observer at the equator can only see half the available constellations at any one time, and it takes a full year to see all of them. Conversely, an observer at either the North Pole or South Pole would see half of all the constellations every night.