Once you've transferred funds to your Futures Wallet you need to transfer the funds to the respective Trading Wallet to start trading.
You can do this from the Wallets-tab on Kraken Futures:
Click on "Transfer" for the cryptocurrency/digital asset you wish to transfer to your Trading Wallet and input the amount.
The destination depends on the instrument you wish to trade. For example, Bitcoin can only be transferred to margin accounts which use Bitcoin as collateral (XBT:USD Margin and XRP:XBT Margin). These funds can then be used to trade PI_XBTUSD, PV_XRPXBT, FI_XBTUSD and FI_XRPXBT. Once transferred the available margin will increase, allowing you to start trading:
The balances will also update in logs section of your account:
In order to withdraw funds, you have to transfer the funds to your Futures Wallet and then to your Spot Wallet on your Kraken account. See our guide for transferring funds between your Spot and Futures Wallet.