Hey there Kuzu,
It can also be the item descriptions that are not good enough to explain.
But basically the effect of the Dagger and Kite Shield only activates when you Parry and Block respectively, the difference is that without them, you can only Parry and Block the enemy you choose, while with them, the Parry and Block will work for every enemy in the same turn.
Stunning has 2 benefits:
- It removes 1 source of damage for 2 turns.
- It allows to freely attack the stunned enemy without him being able to counter your attack.
Since you can only target a single enemy, it means the others are free to act against you on that turn.
I don’t know if this covers you doubts, there is also the TUTORIAL section in the About screen within the game, it may contain helpful information regarding this.