What are these contests?

I don't get this thing. What are these weekly contests (the winners of which are listed on the home page)? Where can I access the contests? I can see no link where I can view the contests. I can just see the winners.

And now who are these senior members and how are they nominated? And how do I know if one's a senior or not?

To become a senior member, you need either a silver Poet's award or a silver Favorite's award, I believe.