Mandy there are some tools and ideas here that can help you; look around the different forums. I think making small changes is best at first. Try things like 1) eliminate all the junk food and fast food; 2) get lots of fruit and veggies and other healthy snack foods; 3) go for a walk each day.
That's a good start for now; until you find a gym or other kind of exercise that you like to do. Cheryl ... talk about calorie-counting, when I found out how many calories there are in a slice of pizza, a large fry, milkshake, or a big hamburger, I was shocked too. There are some foods that I will never be eating again. Instead, I make my own lower-calorie versions. You'll find some great recipes here too.
Jump right in, read a lot, post often; and you'll soon be on your way! I just know that you are going to love it here ~ a fellow encourager ... Rosebud.