This Achievement is earned in career mode on the PGA Tour Season. It will unlock once you win your first major tournament.
There are four majors: EA Sports Major, US Open Major, UK Open Major, and PGA Tour Major. They are easiest to win on lower difficulty settings with a single round (this is set at the start of each season and cannot be changed midway through). Winning one will also put you 1/4 of the way to unlocking the "Grand Slam" Achievement.