What does “myArr[0][2] = 42;” here mean?

Question

public class Program {
public static void main(String[] args) {
int[ ][ ] myArr = { {1, 2, 3}, {4}, {5, 6, 7} };
myArr[0][2] = 42;
int x = myArr[1][0];

System.out.println(x);
}
}