Perhaps you're wondering what nested lists actually are. Let's use an example to find out.
Suppose we organized a fundraising event that raised funds in four different places on three different days. We could store the amounts collected in each place on each day in separate lists, like this:
donations_day_1 = [345.0, 287.80, 119.27, 329.30]
donations_day_2 = [294.25, 349.0, 178.90, 262.34]
donations_day_3 = [401.0, 456.45, 289.43, 319.27]
This, however, is a very verbose and inefficient way of storing data. It's better to use a nested list:
donations = [
[345.0, 287.80, 119.27, 329.30],
[294.25, 349.0, 178.90, 262.34],
[401.0, 456.45, 289.43, 319.27]
This is a nested list. As you can see, each list has now become an element in an outer list. Single lists are separated with commas, just like any other type of element in a list.