So how exactly does the rank/lp system work?

I'm just getting confused now. One game I'll get 24 lp for beating kids that are Silver V, the next there's Gold IV's, and V's, and I get 17 or 18. That's not even mentioning that why am I playing a Gold IV, when I'm in Silver II? To me, at least in lower levels, Gold's should generally play with Gold's, Silver with Silver, ect. Maybe I'm completely wrong, but this season has just seemed kind of weird with who I'm playing against.

Also, side note, are there that many people with boosted accounts, or that many that have bad placements, but I'd say one out of every 4 or so ranked games I see someone with a Plat border? Being my ELO, you'd think it'd be pretty hard to have that many getting poor placements.