Transmitted messages from the gateway

Hi everybody!
I’ve some questions about the meaning of transmitted messages from the gateway. I suppose they are sent by the gw but Where are these packets sent and why are they sent? In addition, I’d like to know how can I send messages from my gateway to an especific node and whether this is possible or not.
Best regards.

there’s a lot of info ‘out there’ … search terms include LoRaWAN