I tried look in the Roblox Wiki but I couldn't find anything relevant to my problem! So I am trying to make a script that print a message in chat every time a player joins the game. I know how to fire the script every time a player joins the game but I don't know how to make the script print a message in the chat log.
That isn't possible with the ROBLOX chat. People just make custom chat systems if they want to do that, just like Dalek said.