Hard to sum up into subject so:
How do you make it so when you enter a command, it displays a chat message, you enter something, then the command finishes? Take for example the scale changer, enter the command, it asks a scale, you put "2 2 2" or something and it sets it to that.
And:
How do you include 2 variables? Example: *enters /register* "Name?" *enters name* "Job?" *enters job* "Your name is now: [name] and your job is [job]. Congrats!"