Proto-Indo-European is the common ancestor of many of the India and European languages spoken today. Little is known about it, because it wasn’t a written language, but linguists have traced languages backwards, using their knowledge of how languages evolve, to reconstruct what PIE probably sounded like.
Because there are no written records, nobody even knows for sure how long ago it was spoken, or where it originated, but the theory is that it dates back to between 5000 and 2500 BC and that the speakers lived around the Black Sea area. From there they probably migrated across Europe and Asia and the language evolved in different ways to the languages we speak today.
I came across this article a while back and found it fascinating. Have a look and listen to what Proto-Indo-European was probably like! Telling Tales in Proto-Indo-European – Archaeology Magazine.