To lock an object, take Locker in your hand and then dip the tip of it into an object you want to freeze and press the trigger. The object will turn light grey and will no longer respond on touch and press. To unlock, press on the object again with Locker.
You can switch between three modes using Stick / Touchpad on your controller:
Lock & Unlock
Lock Only
Unlock Only
Supported list for locking
Imported static models
Imported image refs
Imported video refs
Predefined static model assets
Text Tool and some other tools (cameras, lights etc)