A hook is defined via a hook name. When the server runs certain actions it will also run all hooks registered again that action's hook name.
server_channeltext( integer playerid, string channel, string message)
Is called when ever a chat message is sent from the server to the client.
Is called when the server starts a new game.
Is called when the server starts a new round.
Is called when players are actualy make there moves (either buying or aiming).
Is called when the overall score screen is being show (at the end of the match).