Let's configure the Wireless Lab network to use Open Authentication and no encryption. This will allow us to see the packets using Wireshark easily:

Let's connect a Windows client to the access point. We will see the connection in the airodump-ng screen:

Now, on the attacker machine, let's run a directed deauthentication attack against this:

Note how the client gets disconnected from the access point completely. We can verify this on the airodump-ng screen as well:

If we use Wireshark to see the traffic, you will notice a lot of deauthentication packets over the air that we just sent:

We can do the same attack by sending a Broadcast deauthentication packet on behalf of the access point to the entire wireless network. This will have the effect of disconnecting all connected clients: