It’s not as if there was a time when people gathered and decided to launch the Russian state. However, there was a time, place, and a person who consciously created the foundations of the Russian state.
There’s more than one answer to the question, “When was Russia founded?” because there were, so to speak, several different Russian states throughout the course of history.
The first date is 862, when Rurik (and, probably, his brothers or aides Truvor and Sineus) was summoned by the people of Novgorod to rule over their lands and protect them from enemies. Historians trace the history of the Rurikid dynasty from this point in time.
However, foreign chronicles referred to the people who lived in the Northern Black Sea region as “Rosses” (росы) even before 862. The Annals of Saint Bertin, covering years 830-882, mention “people of Ros” and their king under 839. Then in the 10th century, Byzantine Emperor Constantine VII Flavius Porphyrogenitus (905-959) mentions pechenegs (nomadic people of the Northern Black Sea region) waging wars on Rosia and attacking their capital, Kiev.
