You really should read through whatever study material you are using, you seemed to have missed some crucial knowledge. Have a read through the site's C Tutorials. As for your immediate questions:
Code:
#include <stdio.h>
int main(void){ //note how main is defined
int num1, num2, result; //note descriptive variable names
printf("Enter two numbers:");
/*scanf takes pointers to the variables
to store the input. Note the use of the & operator*/
scanf("%d %d", &num1, &num2);
result = num1+num2;
printf("Result is: %d", result);
return(0); //Note returning a value to the OS
}