The challenges are intended for all Anim8or users, no matter what your experience level. The point is not to win as such, but to further your knowledge and understanding of the software and share this with others. I have often voted for entries that might not have been the most polished or technically amazing, but had an interesting and unique take on the challenge guidelines, or demonstrated a sense of humour, or a dynamic and interesting camera angle.
I have learned something from every challenge I have ever entered, on this or any other animation site, from my own experiments into how Anim8or works as well as input from others, and I strongly believe that my own learning curve was greatly accelerated by these challenges. My advice to you is don't worry so much about what you do or don't know about Anim8or yet, if you are here on this site then you are interested in 3D design and animation, and therefore we (the Anim8or community) are interested in seeing your stuff, hearing your opinions on the work of others, and helping you get better at Anim8ing.