How to create/destroy object?

[665afb09b5c22minister]

Hello! I need the advice!

1.How to realize the following:
-you have a button
-you press the button and a desk was created immediately before you
-you press the button again and the desk immediately disappeared
2.And this:
-you have a button and a robot
-you press the button and the robot starts to attack you
-you press the button again and the robot becomes friendly to you
Thanks!