This HelloWorld program is for the serial flash memory mounted on the Wi-Go board. If yours isn't mounted on it, then you probably will need some other pin definitions.

To use this program plugin both the openSDA USB port and the KL25Z USB port. Use your favourite terminal program to listen to the com-port generated on the openSDA USB port. The KL25Z USB port will emulate a USB MSD device.

Load this program, reset the board. If everything goes correctly a pop-up will appear that the drive needs to be formatted (tested on Windows 8, but I assume it is similar on other OS'). This is because the flash memory is completely empty, no filesystem is available. Just use standard settings (512 byte sector size), and format the drive. When this is done reset the board again.

This time it should load without popup, and after a small pause the flash drive should appear on your computer. On it is a single file, open the file, write something, save the file. Whatever you wrote should appear in your terminal program.

Aditionally the other way around also works, write something in your terminal program, hit enter, and a file is created with whatever you wrote in it. IMPORTANT: In TeraTerm you need to have transmit settings on CR+LF! (Found in Setup > Terminal).