Our HID readers, store a set of default security keys, which can be selected using the Key Slot 0 drop down from halfway down the app page. These keys are used for authenticating data access to the cards. You can overwrite these default keys using the top section of the app page. I.e. select the key slot you want to overwrite, fill in the text box labelled Type hex key to load and press load key. The Persistent checkbox will permanently overwrite the stored keys on the device, unless you are really sure on what you are doing I would avoid this.
To read/write data to the card type the block number you want to talk to in the Enter block number textbox. Press the Select Card button, this tells a card in the field that we want to talk to it. Select the corresponding key slot for that block, and then authenticate. On successful authentication you can then read/write to the block.