Hi,
Welcome to the community.
When a call is placed on hold, only the caller who put it on hold may retrieve the call. This is where parking functionality comes in. It allows you to park a call at various parking locations. To do this you must do a blind transfer to *0 and the number you want to park it to 1,2,3. Once you have "parked it" you can notify a user of what number the call has been parked to and he may retrieve it using *1 [parked number] to pick it up.
So to clarify parking at location 1 for example
User recieves call and does a blind transfer to *01.
User who wished to retrieve the call must simple dial *11 to pick it up.