While aboard the Cylon Baseship, Anders' condition releases a flood of visions and crucial memories.

The 13 tribes consisted of humans and cyclons, who then traveled to Earth at regular speed, with a huge elapse of time between the growth of the Kobol Colonies and the 13th tribe of Cylons going to Earth and settling. Then when the Earth Cylons found out that the twelve tribes would be attacked by Centurions, they agreed to help re-create Resurrection technology for the Centurions if they would stop fighting the other tribes.

Why did the original 13 tribes create cylons first and then the metal Centurions later? He said that the twelve tribes invented organic memory so does that mean they were humans with the name Cylon, or were they invented? And I thought the 13 tribes were from Earth and then colonized Kobol with one tribe leaving back to Earth?

Hot Dog being Aaron's father = retcon, IMO.

The way I understand it, the 13th tribe was a Cylon tribe, not human at all, created by the humans and/or Gods on Kobol. In the mythology of the show, the 13th tribe leaves Kobol 2,000 years before an environmental event (possibly a flood, according to Pythia) causes the 12 remaining tribes to leave Kobol. Don't forget that in early season two, Head Six tells Baltar that Kobol is very different in meaning to the Cylons than it is to the humans; to the Cylons, it's an evil place where human sacrifice occurred. It's possible to infer that the human sacrifices were part of the attempt to create human-like Cylons, i.e. the Final Five and the inhabitants of Earth.

The 13th tribe was a form of Cylon, as evidenced by the tests they performed on the remains found on Earth, but they are different from the later models of the 12 colonies; for example, they could reproduce. It was said that through their procreation, they lost their capabilities of resurrecting with each successive generation, so the Final Five were tasked with re-creating that ability. Then Earth is attacked, by whom it isn't entirely clear yet (other Cylons?), and the Five resurrect in a ship positioned near Earth.

The Five then embark on a journey to find the other 12 tribes in an effort to warn against the creation of AI, but they don't have FTL capabilities, so it takes them 2,000 years to find the colonies. When they do, they discover the ongoing Cylon War. They offer to help advance the Centurions in biological form if the Centurions agree to end the war. Then the skin-jobs of their creation turn against them to complete the annihilation of humanity.