This formula returns true or false for each comparison, on each row.
So on a row with a value >=100000 in column E, the first section returns true
if the value is also <=199999 in column E the second part returns true, and if column K = 1 the third part returns true.
True evaluates to 1 and false evaluates to zero.
Thus if any of the three parts is false the row evaluates to zero (as anything times zero = zero)
If all three parts are true, the result is 1 * 1 *1 which is 1
SUMPRODUCT sums the results from each row in the range, and in this example returns the number of rows matching all three criteria.
If instead of hard-coding values into the formula you use references to other cells, it is easy to create a table showing the number of rows matching sequential ranges with or without 1 in column K.