Party leaders are interviewed by the president and recommend someone to be PM. If party leaders representing a majority name one person, that person is named to form a government, naming the heads of departments and coalition members.
If there’s no majority, the president appoints someone to give a first try at forming a coalition. If that fails, someone else can be given a chance.
Netanyahu is going to be tapped by President Rivlin because he’s the leader of the largest party.
Gantz was stupid in turning down a national unity government last year. That ship has sailed.