Different species of humans

I am having a hard time understanding the difference between species. I thought that in order for something to be considered a different species it would have to be so different to the point that one species could not have children with the other...

species. So this would mean that a H*mo Habilis or a H*mo Erectus could not have children with a H*mo Sapein. Is this why they are considered different species? H*mo Hablilis, H*mo Erectus, and H*mo Sapiens are all considered humans but they are differnt species. So if this is true then Human beings are not their own species? What is a human being if it is not its own species?
P.S. I think somebody should fix the banned words because I had to put a * instead of an O when ever I was referring to H*mo Sapiens, Erectus, Habilis etc. Kind of annoying when that isn't a bad word, but a scientific name that classsifies Humans.

I have no idea but they put the * because people often refer to homosexuals as h*mo's and it's very rude. Next time just make homosapien (etc) one word.

H*mo means same in Latin, or Homogenous, as in a mixture all evenly distributed
(Homogenized milk) H*mosexual, merely means same sex as Hetero means different. There are different species of mankind, but genetically we are close enough to interbreed, usually without any disasterous results (some incompatable blood types, or genetic flaws can affect offspring, within the same species, or cross-species)
There is actually no such thing as race except in Chemistry. In living things
the ordering is as follows: Kingdom (Plant or Animal)
Phylum
Class
Order
Family
Genera
Species (What some incorrectly term race)
The cites you listed (H*mo Habilis, H*mo Erectus etc are different Genera)
They are also (presumably) extinct.
Sorry to have to use the * this program is apparently governed by a very ignorant censor that does not know a correct and suitable word, from a slur or vulgarism
Someone should explain the Latin scientific words to the robot so it doesn't block words used correctly, and not in an offensive manner.

its probably also because there from different periods of time
one wouldnt have even got to meet the other
because they evolved so much over time
although all humans today are still one species,
but, just like animals, there are different kinds of us
(from different countries, and parts of the world)
this is because the enviroment is one pof the main factors for evolution
things evolve to suit there enviroment
but it will still take many thousands if not millions of years for us to evolve so much that we become that different
and by that time wed probably be so far away from each other that all chances of a meeting was impossible

I thought that H*mo Sapiens, H*mo Erectus, and H*mo Habilis were of the same Genus because they shared the same Genus H*mo, which means man.