Where and for what purposes does your permit entitle you to carry and use a handgun? Is self-defence a lawful reason to possess a handgun? What must you do with the gun when you are not using it?
I can carry it almost anywhere that isn't considered a protected building (like a Court or Parliament House).
Is self-defence a lawful reason to possess a handgun?
Not by itself, no. But being a member of a pistol club (for example) is, and if you have a firearm, and you are exercising your common law right of self defence, then you may use a firearm if you have reasonable grounds to believe that you or another person is in danger of death or serious injury.
What must you do with the gun when you are not using it?
Any firearm not in active use or control, must be locked unloaded in a safe. And, yes, that is a problem is certain circumstances.