Thanks for pointing me to the calender where I can find challenges.
I also would like to understand how the challenge trackers work. When I have tried using them the choices sometimes leave me bewildered. The wording can use abbreviations that make no sense to me. I don't know where I can find a tutorial.
edited to add emphasis.
The Challenge Tracker is used in connection with various different challenges. Some are weekly challenges, others for a month. There is even one for just Saturday. You can read about the various challenges here. Scroll down to the Ongoing section and read quick summations. From there if one sounds interesting, click its link and learn more including how to join.