How to display characters on LCD with FreeRTOS
You need the board support package for the EFM32. It should have the drivers for the peripherals on the board, hopefully including the LCD. If it allows you to write plain text to the LCD, then

Call FreeRTOS_open() with the name of the LCD peripheral; it returns a Peripheral_Descriptor_t object (probably just a pointer incognito), or NULL in the case of fail.  This object is the first argument to FreeRTOS_write().  The second argument is a pointer to a char array containing your "Hello World" string, the last argument is the number of characters in the string.