How do you whisper players?

I have tried looking on the internet but cannot find it. Could someone please tell me how to whisper another player in gmod?

it depends on the plugins the server has and the gamemode, default sandbox garrys mod has no whisper command, others servers who do run it use the command: "/whisper “name” “text” or some thing like that, as i said it all depends on the server and mods it or you are running