How do I make a script that detects when I say any message, my character jumps once?

Won't give you full script rather lead you in the right direction. Remember this is not a request site, the point of this site is to get help with a script you've already made, or concepts, explanations on a piece of code, stuff like that.

You can make use of the PlayerAdded event. This event is fired when player joins the game. From here you can get the player who joined.

game:GetService("Players").PlayerAdded:Connect(function(player)

end)

The player class has a Chatted event. This is fired when a player chats.

player.Chatted:Connect(function(message, recipient)

end)

message is content of the message they sent, and recipient is the player they whispered the message to. This will be nil if they didn't whisper.

That's all I'll show you. Now you put the pieces together.