How do I connect a timer to circuit box which controls our outside lights?
From the looks of it, there are only black, white, and ground in the junction box. This most likely means it's set up as a switch, and the white wire is actually a switched hot (and should be marked with tape or marker with a black or red stripe).

Unfortunately, since your timer requires a neutral, this isn't quite going to work.

What you need to do is:


Open the main panel
You should find:

The black from this junction box goes to the breaker
The white is connected to a black wire that goes off to the fixture
The white wire that goes off to the fixture is connected to the neutral bus



If this isn't the case: stop. Update the post, as my instructions won't help.




First, route the wire that goes off to the fixture into this junction box

Ideally, you would do this outside of the breaker panel
You may need to use wire nuts and run a new wire into the junction box

Second, run a new wire from the panel to the junction box

Connect neutral (white) to the neutral bus in the breaker panel
Connect hot (black) to the breaker in question
You may be able to use whatever wire is there now for this, impossible to tell without opening the panel



You should now have in the junction box:


Black + white + ground from the panel (black from the breaker, white from neutral bus)
Black + white + ground going to the fixture.


Basically, just connect it up exactly as that diagram shows: 


Connect grounds together, and to the fixture
Connect neutrals together (including the white wire on the timer)
Connect black from the break to black on the switch
Connect blue from the switch to black to the fixture