Proto-Indo-Europeans is a group of people who lived a long, long time ago before you or your grandparents were born. They were the ancestors of many different cultures and languages that we know today. Imagine a big family tree that goes all the way back to the very first people on Earth. The Proto-Indo-Europeans were like a branch on that family tree.
The Proto-Indo-Europeans lived in an area that is now Europe and Asia, but it wasn't countries like we know them today. It was more like different groups of people who lived in different regions and spoke different languages. They were hunters and gatherers who traveled around in search of food and a good place to live.
Over time, these people began to develop different customs, traditions, and languages. Some of them went west and became the ancestors of many modern-day Europeans, while others went east and became the ancestors of many modern-day peoples in Asia.
Even though the Proto-Indo-Europeans lived a really long time ago, their legacy is still with us today. Many of the languages spoken in Europe and Asia today, like Spanish, French, German, English, Hindi, and Bengali, are all related to the language that the Proto-Indo-Europeans spoke. It's like they left a big footprint on history that we can still see today!