I'm 18 an ddi (didanosine) wanna lose weight about how much should I excercise day?

Realistic goals. Start exercising finding an activity you enjoy. Aim for 30 t0 60 minutes but try not to get burned out in the sense it will be a "chore", watch your caloric intake, you must decrease the calories and increase the exercise in order to "burn" calories. Talk to a nutritionist and find guidance!