Your fighting style you chose at level 1 becomes much stronger, as a reflection of your growing mastery as a fighter. For example if you chose the archery fighting style you gain the Archery Expert ability.

Archery Expert. When you have advantage on a ranged attack you may also make an extra attack as a bonus action. In addition, you gain +2 to damage rolls with a ranged weapon.

Defence Expert. As a reaction to being attacked, you may gain resistance to the triggering attack. In addition, your armor class bonus increases to +2 up from +1.

Dueling Expert. As a reaction to being attacked in melee, you can impose disadvantage on the attack roll. While fighting a creature that isn’t adjacent to any of your allies the damage from your fighting style increases to +4.

Great Weapon Expert. When hitting a creature with a two-handed weapon. Choose another creature within 5 feet of the original target and within your reach. If the original attack would hit the second target it takes damage equal to half the damage dealt to the original attacker.

Protection Expert. While wielding a shield you provide 3 quarters cover to allies if you are standing between them and their attacker. If you impose disadvantage on an attack roll due to your Protection Fighting Style and the attack still hits. You can choose to take the damage instead of your ally.