Okay kiddo, imagine a long time ago there were people who lived in a place called Finland. Before these people spoke the language they do now, they used a different one. This old language is called the pre-Finno-Ugric substrate.
But how did it become the old language and not the language they still use? Good question! Over many years, different groups of people came to live in Finland and they brought their own languages with them. The people who spoke the old pre-Finno-Ugric language eventually learned these new languages and started to use them instead.
But even though they stopped using the pre-Finno-Ugric language, some parts of it stayed in their new language. Just like when you mix two things together, it’s hard to separate them completely. So some words or ways of speaking that came from the pre-Finno-Ugric language can still be found in the Finnish language today.
It’s like a secret code that only some people know about because it’s so old. But it’s still an important part of the history and culture of the people who live in Finland.