You touch your beast companion and can choose to enhance their natural defensive or offensive abilities:

Defensive: Your companion gains +1 to their Armour Class, Savings Throws and Damage Resistance against all attacks.

Offensive: Your companion gains +1 to Initiative, Hit and Damage rolls.  They also gain 10 feet of additional movement.

This spell can be cast at a higher level.  When cast at 4th level, the bonus is +2.  When cast at 5th level, the bonus is +3.