Good on you for making the decision to get fit. It's not easy, I know. I was a very overweight kid and losing all that fat and putting on some serious muscle made me feel unreal. As the more experienced guys have said above, you don't need steroids and it's not going to do your already strained organs any good. Stick to a diet and an exercise routine. PROTEIN: You're going to want to stock up on turkey, chicken, fish, beans, nuts, egg whites. FATS: Poly-unsaturated fats help reduce hunger pain and they're good for you. Olive oil is a decent example, so instead of cooking with butter, use that instead. As for bad fats, it's going to be difficult to avoid them completely but do your best. Fried food is a huge no no, it might feel good for 5 minutes, but for the rest of the day you'll feel awful. SUGAR: Fizzy drinks or soda as you guys call it is as good as poison, it's awful. Can of coke has 10 teaspoons of sugar in (100% of your daily allowance), not worth it. Get your sugars from fruit (pineapple makes the stuff that shoots out of your trouser snake taste quality, so your partner will be spending a lot more time down there which is always a plus!), veg, yogurt and wholemeal bread. CARBS: You need carbs to function, this bull about the Atkins (heart attack diet) is ridiculous. You need carbs, so just be sensible when it comes to it. LIQUID: WATER, WATER, WATER. Drink water, it's all you need. Sack off coke, OJ, lemonade. Go for water. Sugar free cranberry juice is a good option too, tastes good, full of antioxidants and is a diuretic.
You've got to enjoy what you're eating otherwise you won't stick to your diet. After a few weeks of eating nothing but healthy food, your body will crave it. That's not to say you can't go out once every week or so because you should treat yourself or go out, socialize and have a few beers.
As for the gym, I'm sure you know what you need to do. Cardio is obvious and lifting high weight at low reps burns fat like a boss. Bash one off twice a day, get your heart pumping and put a smile on your face, burns calories and builds up your arm.
Above all, be committed. Imagine yourself sitting at your computer this time next year a thin man. It's well within your reach and you don't need juice to achieve that. Do whatever you need to do to stay motivated. good luck bud, you're going to smash it!