High intensity interval training is an increasingly popular form of training that involves short bursts of very high intensity cardiovascular activity followed by very slow and relatively long rest intervals. The idea is that using this rather extreme yet short type of training will cause the body to gain similar cardiovascular benefits as to those gained from long relatively slow runs.
However, this type of training is something that shouldn't be undertaken lightly, especially for those who are just starting to train. While using a bike or other form of low / zero impact machine will have the benefit of reducing the amount of force exerted on the joints which can be problematic to those who are running, high intensity interval training will always place a large amount of stress on the heart. Therefore, it is a bad idea to undertake it if obese or suffering from any heart conditions.
To be entirely honest, HIIT or HIT really wouldn't be my thing personally. If I were ever in a situation where I was trying to lose weight, I would eat more vegetables (they leave you feeling fuller with less caloric consumption) and drink plenty of water (in the times of excess food intake we now find ourselves in, it is very easy to be dehydrated and not even realise it. Chronic dehydrated can manifest itself as a desire to eat more food, perhaps a useful adaptation to have when all food used to be very high in water, but with all the junk food around these days, this is more likely to be a problem than a treatment.) I would also eat my food very slowly as sometimes we can bolt our food down and this means our body doesn't have time to tell us we're full before a whole dinner is inside our stomachs.
So really, while it mightn't mean much coming from a perpetually skinny teenager, my advice for weight loss wouldn't be to try to eat less, it would just be to drink more water, eat more vegetables, and eat slowly. The best way to eat for maximal absorption is to put one mouthful of food in our mouths, then chew this down to a watery paste before eating anything else.