I'M A HUGE TRASH!!!!!!!!!!

To be honest I haven't played in about half a year. I think I stopped at the start of season 6. Anyway how in the world do I learn how to play the game. Back in season 4 I practiced my cs and got around 85 in 10 minutes, or even more. The new mechanics are cool and all but can anyone of you suggest me on how to get better. I don't even mind getting in elo hell, if it still exists. I know that 99% of the time my loses are my fault and I accepted the fact that I'm really bad at this game. Is it still possible to grab 100 minion kills in 10 minutes without runes and masteries like before or the spawn timing was changed??? Should a support still help adc last hit or nah What are the general changes since season 4-5 becuase I need to master new way of playing.