How should i save my money?

i'm 15 years old and i have a job and every week i get a ok pay check about 100 probably more since summers rolling around. and i cant remember what my teacher said like twp years ago something like 10 bucks a week and by the time you retire you'll be like a millionaire i did the math it doesn't work out maybe i missed something he said please help me out i really want to save up. i also wanted to know if i should save like a set amount or like a fraction like 2/3 or something??