OK, it's not difficult. How far have you got and where are you stuck? Do you understand the assignment?
Have you worked out how to represent the flash cards? (for example would a simple array of strings be sufficient?)
Do you know how to get a random number?
How would you determine whether to display question or answer: is that also random?
Having worked out how to represent the flash cards, can you think of a way to combine that with the answers to the last two questions?

If the answer to all those is yes then you should have enough to start coding.