I want my Nexus 7 to know when I'm leaving for work and display the details about traffic and such. But I don't know where I need to add home and commute destination.
Actually you shoud set you home and work address in Google Maps/Latitude. You can do this at least on your desktop by going to http://maps.google.com, logging in with your Google account, and clicking
Google Now will figure out your regular schedule after a while, took a couple of days for me to get the suggestions at the right times.
You only need to enable Google Now.
All other settings are automagically determined by Google after a few days of usage.
Note: You give up a bigger portion of your anonymity for that.