Leviton Vizia 24 hr timer - How do I install?
Your timer needs requires four wires.


Black is "hot"
Red is the load wire, which is only hot when the switch is on (closed).
White is neutral, which allows the timer itself to use power to operate.
Bare/green is safety ground.


The box you're working at, does not have a neutral.  It's what's called a "switch loop", so only has a hot, switched hot, and ground.  

You'll either have to run new cable to this box, or buy a timer that doesn't require a neutral.