Short answers, pulled from the story.
East Slavic settlers flooded across the Eastern European Plain during the 8th and 9th centuries. They moved as farmers, beekeepers, hunters, fishers, herders, and trappers to establish dominance on that vast plain.
The Kyiv culture dates from the 2nd and 3rd centuries AD as the earliest known example. It stood as the northern neighbor of the more developed Chernyakhov culture with rare settlements in unusual topographic conditions.
The Primary Chronicle lists twelve Slavic tribal unions including Polans, Drevlyans, Dregovichs, Radimichs, Vyatichs, Krivichs, Slovens, Dulebes, White Croats, Severians, Ulichs, and Tivertsi. These groups consolidated into Kievan Rus' during the first millennium AD.
Disintegration of Kievan Rus polity occurred in the 11th century resulting in considerable population shifts and distinct identities for Ukrainians Belarusians and Russians. Southwestern and western Rus became subject to Lithuanian and later Polish influence while Russian ethnic identity developed in Muscovite northeast and Novgorodian north.
Y chromosome mDNA and autosomal marker CCR5de132 show East Slavs genetically very similar to West Slavs. Significant differences exist from neighboring Finno-Ugric Turkic and North Caucasian peoples all the way from west to east.