Can someone explain how the ranking system works

I see alot of people around the web saying they are doing bad to mediocre (losing majority of matches) in their first 10 matches and getting platinum/diamond/onyx. I would like to think i did pretty well in my first 10 (won majority, had a very high average KDR, average to above average objective completion) and got placed in gold 1. Am i missing something?

Im also confused why unrank people are paired with diamonds and the like when they are trying to become elegible for their rank. Some people get matched against golds while others against onyx? that doesnt seem fair to me. Not that it really happened to me.