Ghost of Tsushima: Quick Attack
Ghost of Tsushima's Quick Attack is a mechanic that enables Jin to quickly inflict damage to his enemies though at the price of lower damage and no stagger effect at the target. It enables you to chain such quick attacks to put pressure on the enemy.
You can execute a quick attack by pressing the Square button.
Quick attacks are executed from the current stance of Jin. There is minimal wind-up and they are executed instantaneously. There is no staggering impact on the target though.
You can compare it with a Heavy Attack where there is a wind-up and a staggering impact, though at the price of a slower animation.
Heavy Attack
We can divide the flow of a heavy attack into three stages. First, there is an extra animation where Jin pulls back to give extra force to the attack. While doing this, the enemy can hit you, so time it well.
The moment a heavy attack lands on an enemy, a meter will start gaining a build-up, accumulating based on the attacks you hit him.
You can imagine this as something similar to Sekiro's Posture mechanic as shown below.
With enough number of attacks, the posture will become broken
Similarly, in Ghost, once the meter is filled up, a large impact animation is shown and the meter is broken.