Flash some lights!
Follow this guide: mbed setup.
Flash lights in an exiting manner, perhaps you write something in morse code!
Use the buttons to the lights on and off.
Hint: Components on the board
Pretend you are a keyboard.
Guide: Make your own mbed keyboard
Use your new-found mbed keyboard knowledge to make a PC volume controller using the buttons on the board.
Use AnalogIn eller DigitalIn to read data from external peripherals like a potensiometer to control the PC volume.
Overview of Pins on the board: - EFM32 Giant Gecko: https://developer.mbed.org/platforms/EFM32-Giant-Gecko/#efm32gg-stk3700
EFM32 Happy Gecko: https://developer.mbed.org/platforms/EFM32-Happy-Gecko/
Nordic nRF51-DK: https://developer.mbed.org/platforms/Nordic-nRF51-DK/