How long till I see results?

Okay , so tm Im starting a diet . I rlly dnt know exactly what to do for my diet so if you know some things I could do , please tell ? Im 13 yrs old , 5'8" and I weigh bout 149lbs or somethingg like tht , and all my friends are like rlly tiny ! So Im trying to lose weight so I can look okay in a swimsuit this summer :) Tht would be amazinggg ! But heres the thing , I have like barely anyways to excersize ! I have stairs I guess tht I could climb and I have an excersize ball but everytime I try to use it I fall off ! Haha , Imma be getting an elyptical (<-- or however you spell it) in April and Im going on vacation in May ! Is it possible to do like 25 mins a day and still see results ? And I cnt walk around bc I live in northern Ohio and its like freezinn ! But I will be walkin around like everyday when it gets warmer bc thts juss what we do . So please help I rlly wanna lose this weight ! Thankss :D