You forge strong connections with animals. You can spend 7 days of downtime regularly interacting with a normal animal (not a companion or other special animal) that is friendly or helpful to you. After this duration, attempt a Nature check against the animal's Will DC. If successful, you bond with the animal. The animal is permanently bonded to you until you form a bond with a different animal or do something egregious to break your bond.
A helpful animal is easier to direct. If your bonded animal is level -1, it gains the minion trait, allowing you to command it more efficiently. The maximum level of creature that can be your minion increases to 3 if you're a master in Nature and to 11 if you're legendary.
Special
You can't have both a bonded animal and an animal companion (though you can have both a bonded animal and a pet or familiar).
Source: Pathfinder Player Core, p. 253
Bring Bonded Animal into a Pathfinder 2e game with The DM Screen.