Believe it or not, but in another part of my life I was a fitness instructor and personal trainer so if you want info feel free to PM me. Basically, you really need to decide what kind of physique your hoping to achieve. If you just want to have well defined musculature without bulking up too much then, as others have suggested, jogging, bike riding, push-ups, sit-ups/crunches and a couple of lightish dumbbells will get it done. What you are looking for there is lots of cardio work and many repertitions with light weights. With your dumbbells you can do bicep curls, tricep kick-backs, overhead presses for your shoulders, and if you have a suitable bench, flys for your chest and reverse flys for your back. It's important to work all your muscles or you'll look odd and it may cause physiological problems, especially if you're working one muscle group hard and not doing anything with their opposing muscle group. So work your triceps as hard as your biceps and your back as hard as your chest.
If your goal is to pack on some muscle then you are looking at lower repertitions, say 10-12, at a weight that is heavy enough that you'll struggle to get the last rep. in. And you need 3-4 sets of these repertitions. That probably means a gym membership or buying a decent weight set with a bench press than can be adjusted to allow you to do inclines as well as shoulder presses. Probably cheaper and safer to join a gym where someone will always be on hand to spot you, because working to failure with heavy weights, alone in your garage is a recipe for disaster. You also want to mix in some cardio but probably not as much as the above case because it will take energy away from building your muscles.
Whichever path you go down you're looking at 3-4 workouts a week and a good, balanced diet should provide you with ample protein at this stage. You really only need extra protein, like from supplements or extra meat/eggs, etc., if you want to do some serious body building. If you go down the muscle building path you should put your scales in the cupboard for a few months because the fat you'll be losing will be offset, or maybe even exceeded, by the muscle you're gaining. Muscle also requires far more energy to support it than fat, so even just sitting around, your metabolic rate will be increased and you'll be burning more energy. So perhaps you want to forget dieting, while remembering to eat a balanced diet, for a few months while you bulk up, then when you want to, the fat will just peel away with a bit of dieting and increased cardio, to reveal chiselled muscles. Most body builders, in their off-seasons, will have quite alot of fat on them because they have to eat so much to maintain all the muscle they have as well as produce more. But once a competition comes around they can shed the fat at an amazing rate because their metabolic rate is so high.
Also remember to vary your program because the human body is very good at adapting to the challenges you set for it. So every couple of months change the exercises you are doing, the order you do them in, that sort of thing.
I don't know what you currently look like and I don't really know what you want to achieve so that's why I've kinda given you too much information. If you do join a gym, they'll fill you in on all this anyway, but hopefully I've helped in letting you know what you're in for.
