I Have Black Lines Under My Eyes. How Do I Get Rid Of Them?

I think you are getting a lot of sleep and your eyes are irritated and puffy from oversleeping. These black lines or circles are probably prominent blood vessels which become more noticeable.
You should also buy Eyecon by BENEFIT. Its very useful and also try drinking a lot of water.

If you want to be all about nature ; try natural remedies, of course - by using tea-bags & hot water, or a cold spoon. Or icecubes work more efficiently, but they can be painful & uncomfortable] Warm some water in a cup, but don't make it too hot. Dunk the tea bag in the warm water, and let it soak it up for a bit. Take the tea bag out & place it on your eyes - laying down. Leave it there for 10-15+ minutes. It probably wont be dramatic, but it will do some justice. Same with the cold spoon, [if you really want, you can put it in the fridge for a while], put the cold spoons under your eyes, where the undereye-bags are & hold it there for 10-15+ minutes, or until they become warm. This should help. FOR A NON-natural remedy, you can try a good old concealer stick. Try to get three shades lighter then your skin, but don't go too light - because it will only further emphasize your bags. When testing, too - make sure you test it in natural sunlight. Because, most of the time, the stores light wont reflect the foundation as it would in natural light.

I have severe black lines under my eyes what medication erases them all of the way.

Black lines or dark circles?  If it's the latter, I have discovered this stuff called Ooh La Lift by Benefit that I put on before my concealer.  It kind of has a lightening thing in it, so that your concealer doesn't make your eyes look darker.  If you're talking about actual lines, maybe you forgot to take off all your eyeliner or mascara from last night! : )