Applying Will

Willpower is mental power similar to how strength represents physical power.

Fire-Making Charm, require a fair amount of willpower to successfully cast. 

Wand-Lighting Charm don't require an effort of will to successfully work.

like pushing on a heavy box, but with your mind

Levitation Charm

The Levitation Charm requires minimal power when you first learn how to
cast it, but if you want to lift heavier objects, you must expend a
greater effort of will.

Sticking Charm

used to stick one surface to another, whether this is two halves of a container, a lock to a door frame, or posters to a wall

Without a sufficient amount of effort, the charm will not function at
all. Even if your will is strong enough to make the charm work, it will
not last very long unless you train yourself to use more magic. A good
casting of the spell results in a bond that lasts for several days, or
even weeks if cast well enough. 

countered with the Unlocking Charm, though the better this spell is cast the harder it is to counter