Transfert a call

Hi !!!
I’m developping a samm PHP Script to transfert a call, with API I can use transfert command but, with this command need a free Channel, so When I want I want to transfert A to C, C must Hangup his phone, or the Call Will be Loosed. I Heared that with Parked Calls I can do it, I Undrestoud How it work using dialplan, but with API I don’t how to do it, can any one help me please.
Thank you