From unranked to silver II?

So, im level 34 been playing for like a month and i dont get too good scores at games. But at friday i started playing ranked and at the evening i got placed in Silver II with 5 wins out of 10. My friends are pretty good at the game but they are all silver V and they say that you get the rank based on your wins out of the 10. So how did i get silver II from winning only 5 out of 10 and having bad scores almost everytime? And is it easier to get a better rank at preseason?