How does preseason work and translate into the new season 6?

So i just started playing the game tail end of season 5 and got to silver 5 and finished there. I would say i'm an average player not horrible but also not amazing haha. And recently my friend got 30 and we have been doing DuoQ and well based off of alot of toxic players and bad plays on our end(few) we have had an 7 game losing streak. I've never been more pissed off at a game in my life tbh haha but then it shot me all the way down from s5 to b1. How and why did it shoot me down so low and how will this affect my season 6 starting point? I dont understand and im definetly not a b1 player haha but im just frustrated with the game and looking for some help on how this will translate into season 6 because since i'm very new to league this whole ranked season crap is new to me! Any help would be GREATLY appreciated on how this works!!

Thanks from the guy who rages too much ~Kyle