I have made a javascript website to play Flecks. Unfortunately, the game cannot yet be played against the computer (for this would take me quite some time to implement). So the website is just for playing the game with two persons. The website version of the game corrects illegal moves, so it might help you understanding the rules of the game.
There is also a Windows program for playing the game. (Hopefully your Windows version and your antivirus will not block the download or block running of the program. Because I wrote the program myself, there is no authentication for trusted software.)