Hey there. Welcome. I'd start by reading the sticky posts in the various forums - there's great information there to help get you started.
Ultimately what it's going to boil down to is what you eat. Exercise is great and you should definitely exercise, but when it comes to losing weight (and not gaining it back) getting control of your eating is probably 80% or more of the battle.
For a lot of people simply cutting out the junk food, the sweets, things like chips or french fries will make a huge difference. Take a good hard look at what you eat every day and I'll bet you can see where you can remove some bad stuff and eat some good stuff.
One thing to keep in mind is that losing weight and keeping it off doesn't mean you can't EVER eat junk food. It just means that junk food can't be something you eat every day or even every week. Junk food, candy, and all those things are TREATS ... not meant to be regular meals. So don't take an "all or nothing" stance. Think about eating healthy over the long term.
Hope that helps give you a bit of a starting point!