An array is a contiguous area in memory; the stack to be specific.
creates an array of integers with 16 elements. The elements are quick to access via indexing or pointers.
int third = myArray; // 0, 1, 2 <-- 0-based indexing
If you need to store similar elements and you know how many such elements you have, an array is a handy solution.
E.g. if you know that there aren't more than 30 students in a class, you can store them like this:
// student name, address, DoB, etc
unsigned int numStudents = 27;
You can also store how many students you actually have filled up in the mathClass.
I hope this helps to understand what arrays can be used for.