[steve d]

"you type in printf("Hello World); and that should do it.

That won't do it, you forgot closing quotes.
printf("this gets printed: first number = %d, second number here= %d\r",first_number, second_number);

When it sees the %, it prints the first_number, then the words agian till it sees the next %,.. The %d is a format descriptor, there is %s for strings,... google on printf format.