The Eredar were the normal race on Argus - But then Sargeras came and his followers became Man'ari Eredar. The followers of Velen became the Draenei, then some of the Draenei became Broken (I don't know why) and some of the Broken became Lost Ones...
Eredar - The first ones
Man'ari Eredar - Demonic Eredar like Archimonde
Draenei - Holy Eredar that fled with Velen
Broken - Mutated Draenei, not sure how they become these
Lost Ones - Further mutated Broken, not sure how they become mutated...