Props are separate objects; you want your character to be able to let go of a sword or a shield.
I'll try to explain the process:
First of all make sure that all the parts of your object are grouped.
Now... you parent the group to a locator and you check that the locator is moving the group.
Done? okay, now you have to create another locator and parent that to the controller of the hand of your character. This usually results on an IK sort of controller.
After that you parent/constrain the locator of the sword and the locator of the hand.
This should allow, when active, that the controller of the sword controls the hand so you end up with some sort of IK control which is convenient whenever there are interactions that require simulating weight.
On the attribute editor you will now have an extra tab. You just 1 to activate and 0 to break the connection.
On a side note i will advice you patience because you are gonna experience a lot of frustration here.
It's a trial an error thing the first few times to get it right because the direction of the parenting is important and parent/constraints direction is opposed to regular constraints.