Transferring funds from one bank account to another is a common business activity. The approach is the same, regardless of whether you are processing a bank statement or entering the transaction manually.
All you need to do is process a Receive Money transaction into the receiving account, e.g. the Saving Account. When entering this, select the offsetting Account in the transaction screen to be that of the sending account, e.g. the Current Account. If you are registered for VAT, then ensure the VAT Rate is set to No VAT.
Once the transaction has been saved, the funds will appear in the Received column of the Saving Account and the Spent column of the Current Account.
The same result can, of course, be achieved by processing a Spend Money transaction in the Current Account.