For those that are just learning, like me.
Composition: Scoring in this area is based on basic composition of a picture and includes the rule of thirds, balance, cropping, and curved and diagonal lines. Subject matter that does not lend itself to the picture or otherwise unwanted is also considered here.
Originality: Scoring in this area is based on pictures or concepts that I have seen, as well as how much effort you have invested in the picture. Usually a little something that sets it aside from a snapshot. Does it make me want to come back for another look? You know things like that.
Technical Aspects: Focus, exposure, lighting, and other special effects (done by the camera), and post processing are all considered in this category.
Meets Challenge: This is based on my interpretation of if you, have/have not, met the challenge. This is fairly simple but quite important for this site.
There are many sites that can give you assistance in achieving better skills in photography, but I think the best way to learn is to take pictures and show them to other people. Believe me when it is a good one you will know it.