How do you start a succesful business on ebay?

I am 18, and just got out of highschool, and i want to start a business on ebay, so i could get the job i want without having to worry about not making alot of money (its working with horses). anyways, what are some of the things i will need to actually make profit? and the things to research before doing it? i dont want to just buy low, and sell high, i think thats stupid, but i was thinking of getting a manufacturing licence or business licence (idk which one i need) so i can buy from the manufacturer, and sell it at market price. is this a good idea? thank you so much for your help!