Karol Nawrocki has not decided on election mode. What is it and how is it applied?

The Law and Justice Party-backed candidate in the presidential race did not opt for election mode after Monday's Onet publication about him. "I anticipate Mr. Karol Nawrocki to immediately turn to court," he said. - Prime Minister Donald Tusk says. And what is election mode and erstwhile can it be used? We explain.