If I eat one twinkie everyday will I gain weight?!

Not unless it contributes toward the amount of Calories you consume and it is more than that you expend.

It depends on everything else you're eating. If you're eating pizza, chips, soda, candy, cookies, and other garbage everyday along with that and no physical activity, then yes you will probably gain weight.

It depends on how much exercise you do and the rest of your diet. Twinkies aren't even that bad for you. Your average cookie is worse for your body.

I would advise against it, try every other day, and work your way up to once a week.