Starting A New Corporation

Is it determined by the percentage held by each partner or is it decided by the partners as they prefer?
By owning the majority shares automatically makes you "president" of society?

Officially? The board of directors. However, the shareholders elect the board. So if you are a shareholder majority, you can even name the chairman, president and CEO together, or whatever you want for this question of fact. The titles really mean nothing. It is the responsibility counts.

depends on the partners may change the titles of each year if they are 50/50, but normally the majority shareholder is the chairman.