Parking a call is a common feature of PBX systems for which a caller can be placed on hold and picked up from another phone. This could also be referred to as Call Camping.
To park a call on an InTeleSync phone system, while on a call you should see on your phone a soft key on the display called Park. Simply press that button and you should hear a response such as "Seven zero one" or "Seven zero two". Those are the park slots the call is being placed into. The system will look into the first available slot starting at 701 and going all the way up to 720.
If your phone does not show a Park button while on a phone call, then you can manually park the call by dialing *4, which you should then hear the "Seven zero one" or "Seven zero two" announcement where the call is being parked.
Once the caller is parked, they will then be available to be picked up from anywhere on your phone system by simply dialing the park slot such as 701 or 702, etc. just like you would dial any other extension. The caller will typically be parked for about 120 seconds, but this is certainly a value that can be changed if you like. After the caller has been parked for the allotted time period without someone picking it up, then it will call back to your extension and look like a new call coming in.
Most InTeleSync phones will also include a couple of pickup buttons that may be labelled PU 701 and PU 702, or Pickup 701, Pickup 702. Those are Busy Line Feed (BLF) buttons for monitoring the park slots, and green means the slot is open (no one parked there) and red means someone is parked in that slot.
Your phone system by default is capable of parking up to 20 calls at a time. Yes you can park a call on your own phone, then come back to that call on your own phone by dialing the park slot number or pressing the BLF button. A fancy way of just holding a call while you do other things.