Its basically been said already. When getting into the game, I'd recommend playing some bot games to figure out how to last hit, which is hitting a minion only once when it is at very little health to kill it, learn to harass the other lane, and general awareness of the map. Once you feel you can grasp the simple game mechanics, feel free to move to normal games. Also, thick skin is very important. I play Eve, so regardless of whether or not I do well, I get raged at. So, learn to ignore trolls and acquire awesomeness.
Also, I can in fact help you with two of those champs. As Kog, you will generally want to go bottom with a "support" like Soraka or Sona. You just want to farm all of the creeps you can, and defend dragon. As Lux, I normally go mid. Try to land a E every now and then until you get level six. Then just do your Q>E>R>Auto attack combo. Start Lux with Boots and 3 potions, and start Kog with the same, or a Doran's blade, depending on how confidant you are.
I hope this helped, but incase it didn't, heed previous advice, and go over to "solomid.net" The guides there really helped me, and I'm sure they'll help you. :P