I'll assume you're asking your question for the purposes of finding out what science has to say about when the first "humans" appeared on earth. A strictly religious point of view would obviously differ considerably. Humans belong to the species Homo sapiens. This is the biological name for "people." To answer your question, you need to have some background on what a species is, and a sense of how humans evolved Biologically, individuals belong to different *species* if they are unable to produce children who themselves can have children. For instance, when horses and donkeys mate, they produce a baby that is a little like a horse and a little like a donkey. We call the baby a mule. Mules are sterile and so cannot breed further - with each other, or with a donkey or a horse. Thus donkeys and horses belong to different species. Where do these differences come from and how do they arise? The short answer is that they represent differences in the DNA found in horses and donkeys. DNA is the genetic code which specifies all components needed to "make" an organism. Every cell in your body carries your DNA which acts as a blueprint of how to make "you." Over time changes occur in the DNA. These changes are the result of mistakes made when the DNA is copied from cell to cell, or of more "genetically traumatic" events such as large duplications or deletions in the genetic code (kind of like adding or removing a chapter from one of your textbooks). It's important to realize that these mutations happen randomly. You can't tell when or where a mutation will occur. The effect of these changes is tested against the environment. Beneficial mutations, ones that help the organism survive and have children, are more likely to be passed on to later generations. It's also important to realize that significant amounts of change happen very, very slowly, so slowly that it's impossible to see any change over a person's lifetime. Scientists must look at fossils from millions of years ago to note and appreciate the scale of evolutionary change. Humans evolved from a common ancestor shared both by us and by the apes we see in the world today - gorillas, chimpanzees, and orangutans. This common ancestor is referred to as Kenyapithecus. Its fossils have been found in Africa, and are ~16 million years old, indicating it lived 16 million years ago! Over time (millions of years!), subgroups of Kenyapithecus became sufficiently different that they could no longer interbreed (different species). One of these subgroups led to the line Homo - our direct descendants. Members of the Homo line include Homo habilis which lived ~2.5 million years ago, and Homo erectus which lived ~ 1.8 million years ago. The first humans ( Homo sapiens neanderthalis) are believed to have evolved from Homo erectus approximately 500,000 years ago. Thus, the first humans appeared nearly half a million years ago. Who they were and what they did represents a large field of study, pursued by Archaeologists, Anthropologists and Evolutionary Biologists.