We call that language Indo-European, but we know nothing directly about it. No Indo-European texts survive. Nor is there anything special about I-E in particular. Language families are separate when they can't be shown to contain cognate words. The perception of cognate words is a very inexact science.
Some people see larger-order connections between language families than others can.
We know next to nothing about Indo-European culture, and everything that we know must be inferred indirectly, including the structure and vocabulary of the language. We know a few things about the culture from the words that survive as cognates in modern languages. They worshiped a sky god who was conceived of as a patriarchal Father. There are cognates in widely scattered I-E languages for those words. Our word for a female sheep is ewe .