C :: How To Implement Two Dimensional Arrays

Code:
char str[40][40];
int number = 7;

for (int i=0;i<number;i++){
printf("enter %d th string::",i+1);
scanf("%s",str[i]);
}

Above, I have a little snippet of a code that I'm trying to figure out. I don't really understand how to implement 2d arrays in C that well. But, I mostly want to know is how and where the strings are being stored, especially with the code below.

Code:
for (int i=0;i<number;i++){
printf("enter %d th string::",i+1);
scanf("%s",str[i]);
}

I know that it's asking the user to enter strings, which will be stored into the 2d array. I just don't understand how it's being stored. Will it be placed in the 1st column or 2nd row or something?