When should I workout?

I want to work out twice a day and have a break on the weekends. (Cardio in the morning, 7 minute workout at night.) And that would include just walking and doing simple workouts. Basically, I want to lose weight, feel fit and healthy.

I’m not active at all, I’m 17 and I’m surprised I’m not even overweight. My diet isn’t the best either (which I’ll try to work on).

So, when should I workout? After eating (and what should I eat) or before eating on an empty stomach.