[Singing Boyo]

I'm assuming that by trace you mean that you need to trace the progress of the computation. In that case, change your for loop to this:

public static int sumRange(int start, int end){ //this should be the parameters
     int sum = 0
     if (end < start)
          system.out.println ("ERROR: Invalid Range");//println, not printIn (L not I)
     else
          for (int num = start; num < = end; num++){
          //brackets because you need to print sum, which means the loop will have more      
          //than one statement
               sum + = num;
               //code to print the sum here (same idea as printing the error message)
          }
     return sum;
}

I'll leave you to figure out the printing code.