Hulk has it right.
Before I go any further, let me say that training twice a day is a really easy way to get hurt for a novice, or even an advanced lifter if you don't handle it properly. I got carried away with pulling twice a day, which eventually contributed to a serious back injury.
If you train twice a day I advise one of two strategies:
1. Train heavy both sessions, but with low volume. No more than three exercises per workout. This approach has many advantages in some respects. It allows for much heavier loads to be used. Doing shrugs 1.5 hours after deads, you will shrug way more than if you were doing them .5 hours after deads. In the downtime between sessions, eat, take a contrast shower, apply heat to the stressed areas etc.
2. Make the second workout an "extra workout" as Hulk mentioned. These are done to increase general conditioning and to bring up weak muscles with extra volume. They are also used to speed up recovery. Say you bench in the AM, in the PM you might train abs/obliques and grip, do some light tricep work for extra volume there, then some 20 rep powersnatches for conditioning.
Just proceed carefully if you choose to train twice a day. And before you DO train twice a day ask: Is it necessary? and What will I attain from this?