How would you make Guild_Roster_Update run when somebody joins your guild? I'd assume it would be
but that doesn't work. Any and all help would be appreciated. Thanks in advance
If you're talking about the event, GUILD_ROSTER_UPDATE, you don't. It fires when something in the guild changes. If you're talking about a function that refreshes the guild roster, GuildRoster() is the one.
Side note: If you're going to assume a function's name, Blizzard's convention is <window>_<action> (e.g. GuildRoster_Update()).