There will be a pre-trial hearing and this is where the 'Stand Your Ground' law will be invoked. The judge will ask for a plea and Zimmerman will plea 'Stand Your Ground' instead of Guilty/Not guilty.
The judge will then hold a hearing where the Defense will file for Dismissal on the basis of 'Stand Your Ground' and the Prosecuters will present their evidence to the contrary (if there is any).
The judge will the rule that the shooting was justified or he will rule that there is sufficient evidence to proceed to trial.
In my opinion the pretrial should have been done before he was arrested.
There was zero reason to arrest this man before the pretrial.