In order to play poker for real-money you will need to transfer funds from your Paddy Power wallet to your Poker wallet. If you have funds in your main Paddy Power wallet which you wish to use, then you may follow either of the following methods:
Click on the 'Cashier' button in the bottom-right corner of the Poker client and then enter the amount you want to transfer to your Poker wallet. Click on 'Transfer Funds to Poker Wallet'.
You can also do this from 'My Account' > 'Payments' > 'Transfer' once logged in on the website.
You can use the same methods to transfer funds back to your Paddy Power Main Wallet from your Poker wallet.