What is this new split ranked system?

So, can anyone give me a breakdown on how this works? I ranked up bottom to Bronze 1, then lost 2 games and played jungle, and it said I was up for a promotion. In a panic I thought the two games I just got trolled in got me knocked down. But then I won two games as a jungler and it said promoted to Bronze 1.

So, every role has a rank, but what can you do to rapidly improve them all and have a high average? Can you max out LP and then play one series as that other role to rank it up, or is this one of those weird "Your highest rank is the only one that matters" things? I'm really not looking forward to smashing my face on this brick wall of a trench to have to grind every role up the ladders to get my spot back in Gold/Plat.