These are two theories which scholars believe how Hinduism started and made its way into India...
Aryan Invasion Theory
The invasion theory states Aryan people moved from present-day southern Russia about 2000 BCE in two directions. Westward Europe and eastward into Iran and India. The people who were entering new land are thought of bringing both their religion and language. The outsiders are believed to impose their social order quickly and violently on the older culture. The Ayran people are believed to have broughten the religious writings which are the Vedas,
Aryan Migration Theory
The theory in the Aryan Migration theory is that there was repeated was of migrations into Pakistan and northern India. From all of these different migrants coming were foreign and indigenous cultures the religion of the Vedas emerged.