Lost and need direction

I came back to league after patch 8.12 and I'm lost. i know I'm not the only one but i was hoping somebody could point me in the right direction. I know which champs are really winning this patch, but i have no idea why.

What runes/keystones are really strong right now, and why?

Which items are really shining right now and why?

Like i said, i know which champs, but i have no context as to why they're doing well. Usually the meta shifts around items and masteries, but since i don't know what they are i've been flailing around in the dark and a hindrance to my team.

thanks