I often have the same problem. I always have new players trying to use their quick cast marker for standard attacks.
I would not say I have found the key to articulating it beyond hammering in the point with a sledgehammer. But what I do is just say it is a quick CAST marker. Meaning you use it to CAST spells.
It is not a quick action marker. Usually that distinction helps.
I remind them that attacking with your normal attack is used during your standard activation marker. The black marker is just for using SPELLS.
So I reiterate this a few times, and it usually sinks in after the first round is over.
I would not say I have found the key to articulating it beyond hammering in the point with a sledgehammer. But what I do is just say it is a quick CAST marker. Meaning you use it to CAST spells.
It is not a quick action marker. Usually that distinction helps.
I remind them that attacking with your normal attack is used during your standard activation marker. The black marker is just for using SPELLS.
So I reiterate this a few times, and it usually sinks in after the first round is over.