1) Spawn something
2) Store it in a variable
3) Turn on gravity for that Rigidbody (Make sure it has a Rigidbody)
4) It's going to start falling.
5) Turn off gravity on that object to make it stop falling, or to not fall at all.
If the crane example works fine, its just a matter of looking through it and finding out what is different between yours, then making it work for you.