Bipedality is one of the most distinguishing external characteristics that humans have.
Our ancestors became upright in the protection of the forests, a familiar environment in which they faced fewer dangers. Then, armed with a new type of locomotion, bipedalism, they were pre-adapted to move onto the savannahs and expand their territory. Once we moved into more open environments, we brought a whole package of advantages with us. Our hands were free to make and use tools, we could walk long distances to collect and carry food (and in doing so benefit from enhanced thermoregulation to prevent overheating), we could look over tall grass if we needed to, and so on.
Bipedalism was a behavioral innovation that led the way to making everything possible for our evolution, even if it is still not perfected. Humans continue to suffer from fallen arches, hernias, severe lower back pain, and other bad side effects of bipedalism. But it was still the single step in our ancient past that led to the tool-making, brain enlargement, and intelligence that have led to our preeminence on the planet today.