Okay kiddo, so once upon a time, there were many Jewish people living all over the world. However, sometimes they faced persecution and discrimination because of their beliefs and practices.
One way to look at how many Jewish people there were in certain places at certain times is by counting how many there were in comparison to the whole population of that area.
For example, a long long time ago, in biblical times, Jewish people made up a bigger percentage of the population in Israel - the place where they originally come from - because that's where they were mostly living.
But then, over time, Jewish people started to move to other countries, like Europe and the Middle East. In some of these places, like Poland and Lithuania, there were many Jewish people living there at one point in history.
But then something really terrible happened, called the Holocaust. It was a time during World War II when the Nazis and their allies murdered millions of Jewish people (and others too) just because of who they were. This meant that the Jewish population in Europe decreased a lot after the Holocaust, because so many people were killed.
Nowadays, the Jewish population is spread all over the world. There are still higher concentrations of Jewish people in places like Israel and the United States, but overall the population is much smaller than it used to be before the Holocaust.