Installing GE 20 amp timer?

I bought a GE heavey duty timer to control all the outdoor lights.Im wiring it between a 20amp in the main breaker panel and the single 20 amp box in the shed. The diagram for wiring doesnt make sense. I have 2 black wire, 2 white and the 2 ground. Where do they go?... show more I bought a GE heavey duty timer to control all the outdoor lights.Im wiring it between a 20amp in the main breaker panel and the single 20 amp box in the shed. The diagram for wiring doesnt make sense. I have 2 black wire, 2 white and the 2 ground. Where do they go?

http://www.homedepot.com/h_d1/N-5yc1v/R-202255223/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

http://www.jascoproducts.com/support/manual-downloads/applications/DocumentLibraryManager/upload/15306-Manual-Eng.pdf
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