Three things plug into Cell2Jack. Your home phone goes in the Phone port. The power adapter goes in the 5V in port. Your cell phone charging cable can go in the 5V out port, which is optional and only charges your cell phone while it sits nearby.

Connection diagram The home phone cord runs to the Phone port on Cell2Jack. The power adapter short USB cable runs to the 5V in port. Below the device, a dotted Bluetooth link connects to your cell phone. No wire runs between the cell phone and Cell2Jack. Home phonePower adaptershort USB cablePhone5V in5V outCELL2JACKBluetooth, no wireYour cell phone
The home phone connects straight to Cell2Jack. The wall jack comes later, after pairing works.

Connect the home phone straight to Cell2Jack, not through a wall jack. The wall jack comes later, after calls work. Amazon describes setup as quick and hassle-free.

For the full walkthrough, open the setup page. To pair your cell phone, see pair your cell phone the first time.