A long time ago, there were different beings than us humans. there were people that are not exactly human but are our ancestors, and we evolved from them. there were some that looked more like an ape, and some that looked more human.
these different kinds of people lived differently then us, they were in fact quite smart and resourceful. they made their food by hunting or growing, they were good at building and making things, they also communicated to each other, and they did need to be social just like us.
then we came along, humans. after many years of evolution, the different types of humans started evolving into different looking people, which is were we came from.
but then, poof!, all the other human like species die off, and we are the only ones left.
there is a possibility that the other humans were killed off by a volcanic eruption, because of evidence from the spot.
we don't know everything about these human species, or how they died. but we have found bones and remains of them, and put together evidence of their existence and what they looked like.