Other than your primary weapon, you also have access to a sub-weapon, which uses up a lot of ink but usually has a significant effect, as well as a special, powerful tools that can only be used after inking enough turf. The sub-weapon and special you get is always tied to your main weapon, so even weapons that share the same stats can require different playstyles depending on the sub-weapon they have.
Sub-weapons
Sub-weapons mostly consist of powerful thrown grenades or helpful support items. They typically use up a lot of ink, so they can't be spammed carelessly. The ink pack on your back will glow whenever you have enough ink to use your sub-weapon, serving as a useful visual indicator.
Splat Bomb
Burst Bomb
Suction Bomb
Seeker
Ink Mine
Disruptor
Point Sensor
Sprinkler
Splash Wall
Squid Beakon
Specials
On the top-right corner of the screen is your special bar. It will slowly fill up when you ink turf, and lets you unleash a powerful special when it is fully charged. You will briefly shine and your Inkling's hair will start flaming once you get your special, visual cues visible to both friend and foe. Dying will take a large chunk off of your special bar, so make sure to survive when you have a special until the right moment to use it.