SparkPeople is a lot like Alcoholics Anonymous ;) "It works if you work it." Which means, if you use the tools and support you can find on Spark, you are bound to be successful.
My biggest advice to you would be to not be overwhelmed by the amount of weight you want to lose. Set yourself small, realistic and achievable goals per week / month etc. The sense of accomplishment you'll feel when you reach these small goals, will see you through to reaching the BIG ones.
To start off, I'd suggest walking. It's free, you don't need a gym or any equipment and you can do it anywhere. If you are very unfit, you want to take it easy and slow since an injury early on in your journey isn't the kind of setback you want. Work on 10 minutes every single day, and build up from there. Remember, that any activity you add to your day, anything you're not already doing, is going to burn more calories than you were burning before. So start small and the results will come.
I agree that you have to incorporate strength training, since the more lean muscle you have, the higher your metabolism will burn even when you're sleeping! So maybe get a couple of the beginners strength training workouts from this site to help you get started. You can do this in your room with soup cans, water bottles etc. Again, no equipment needed.
From a nutrition point of view, cut out junk food and excessive sugar and fat, increase fruit & veg and protein and eat regular meals. Eat breakfast before 9am, have small mid-morning & mid-afternoon snacks, lunch and dinner not too late at night. I don't have any "white" carbs at dinner and that's helped me a lot, but you'll soon see what works for you. Drink lots and lots of water as well. These are simple, easy changes you can make that WILL show results.
But you've already done the one thing that is the absolute hardest, toughest, most difficult thing to do on this journey. You've DECIDED to get healthy!!! It's that decision that sees people delay and proscrastinate for YEARS. The fact that you are doing this so young, is a very good thing!
GOOD LUCK and remember that the Spark family is always here to support you. Use it, and lose it ;)