To place a call on hold, simply press the HOLD button.
Once you have pressed the HOLD key, put the receiver back down on the handset. Notice, this will turn the line key orange.
When you want to pick the call back up, simply lift up the receiver again and press the orange line key. This will bring the caller back and you can carry on your conversation.
Note you cannot transfer calls from the hold position. If a caller is on hold and you decide you want to transfer them, take them off of hold (by putting the handset down) and then perform the Transfer actions.