Which is the oil drain plug?
 

I checked on the bottom off my oil sump and I noticed a plug towards the front of the pan and then one towards the rear of the pan (in the direction of the rear of the car). Which is the oil drain for changing oil? Why are there 2 plugs? Thanks.

You can use both to drain the oil. The first plug is for the first slump of the oil pan and the second plug is for the back slump. I normally just drain from the back plug, but you'd be leaving the oil in the first slump undrained.

It doesn't really matter that much

there are two plugs because of the design one plug wont drain all the oil.

Pull both plugs and drain completely. If you don't, you're mixing new oil with some old oil, which defeats the puirpose of an oil change.

Yep, it's not hard, jsut drain everything from one plug, then re-install the the plug and move to the second plug.