KatieMae, welcome to FitDay and the forums.
I was about the same size you were in high school, so I know how it goes. Managed to get down to around 175 at 21, then put it all (plus) back on over the years.
Once you get a food and exercise plan that works for you you'll be amazed at how fast the weight will come off. Good for you that you're doing it now, while you're young--it gets tougher with age!
There's plenty of great people here to lend support. You might check out one of the 100 + to Lose threads (one in Diet Tips and one in the Women's forum). We're also doing a Lose 10% of your body weight challenge by the 4th of July over in Diet Tips if you're interested.
What, specifically don't you get about the activity log?
47 M 5'8"
May 4, 2010...... 440? lbs. (Start FitDay Size 60 Jeans)
June 19, 2010.... 393 lbs. (First Weigh-in)
June 19, 2011.... 229 lbs. (164 lbs. gone in one year :-)
Current Weight... 185 lbs. (Size 36 Jeans)
Next Goal 169 lbs. (07/04/12)
Ultimate Goal 165 lbs. (12/31/12)
The best exercises for weight loss are Fork Putdowns and Table Pushaways.