Generate random numbers based on seed value

Can someone explain to me what seed value is? For example I have this code:

int MIN=0;
int MAX=100;

srand((unsigned) time(NULL));

srand(2020);

int num = (int)(rand() / (RAND_MAX + 1.0 + MIN) * MAX);

I am required to use a seed value of 2020 to generate numbers between 0 to 100. I checked everywhere but seems like there is no tutorial that explains what seed value is, and how the code should change from the default seed value. Line 3 of my code assumes the default seed value, so it does not work with a seed value of 2020. Also, MAX is 100, and MIN is 0.

Thanks in advance!