Your payment code is unique to the wallet and never changes. You can publish and share your payment code without a loss of privacy for you or the sender.
When your payment code is added by another wallet you will be able to receive bitcoin without ever sharing a bitcoin address. You can optionally send bitcoin back to the other wallet without sharing addresses.
A payment channel will be created between both wallets by sending a special transaction on the blockchain. This is called a broadcast transaction and requires 1 network confirmation to confirm.
Once the broadcast transaction is confirmed the payment channel is open. Simply tap the channel name to send Bitcoin directly to that wallet. No need to know their address.