I think most people reading this blog are Romance Writers of America members and are therefore familiar with RWA writing contests, but since I'm planning to post about them all week, I'll give a brief description for anyone else who's here. All two or three of them.
Many RWA chapters sponsor annual contests as fundraisers, mostly for unpublished writers, though there are a handful for published books as well. You send in anywhere from 3 to 60 pages of your manuscript--usually the opening, often accompanied by a synopsis, though there are a handful of contests that judge something other than the beginning, ranging from first kisses to sex scenes to last chapters. Two to four first-round judges evaluate the entry. In most cases, you're facing a jury of your peers, namely other unpublished writers. (Many contests try to have at least one first-round judge per entry be published, and a few have all published judges or only use unpublished judges who've finaled in contests themselves, received judges' training, or who are members of RWA-Pro, a special program for writers who can prove they've completed and submitted a manuscript.)
If you make it into the finals, your entry is then sent on to the editor or agent judging the final round. Otherwise, you get your entry back along with a scoresheet--hopefully filled with useful, tactful, and relevant feedback from your judges!
And those are the two main reasons for entering RWA contests: to get feedback on your writing and to get your manuscript in front of an editor or agent you're targeting.